Introduction
============

Typical carcinoid (TC) is one of four major pathological classifications of neuroendocrine tumor (NET) of the lung categorized by the World Health Organization (WHO). The others are atypical carcinoid (AT), large-cell neuroendocrine carcinoma (LCNEC), and small-cell lung cancer (SCLC) ([@ref-2]). Data shows that bronchopulmonary or lung NETs constitute approximately 25 percent of carcinoma of the lungs, while the prevalence of primary NETs is 20--25% ([@ref-13]; [@ref-22]). Compared with other types of NET, the incidence of TC and AT is lower and accounts for 1--2% of pulmonary malignant tumor ([@ref-3]; [@ref-18]). Another study indicates that there are 10 times more TC than AT patients ([@ref-10]; [@ref-12]). Until now, surgery has been the main treatment for TC, the low-grade lung NET, at the localized stage ([@ref-20]; [@ref-21]). The recommendation of adjuvant therapy, especially radiation and chemotherapy, remains controversial ([@ref-21]).

For early stage patients with operable TC, there is no general agreement on the optimal operation mode ([@ref-7]; [@ref-11]; [@ref-14]; [@ref-15]). Lobectomy and sublobectomy (wedge resection and segmental resection) are the major surgical options for localized diseases. Traditionally, anatomic resection (lobectomy and segmental resection) is considered the best option for patients with peripheral lung tumors, while segmentectomy and wedge resection are widely used for patients who have limited pulmonary function ([@ref-2]). Recently, Taher Abu Hejleh et al. ([@ref-8]), after collecting and researching the SEER data, suggested that the prognoses for lobectomy and sublobectomy were comparable. Some studies have shown segmental resection to be superior to wedge resection in liver cancer and non-small cell lung cancer (NSCLC) ([@ref-5]; [@ref-4]). Other studies found no differences between wedge resection and segmental resection in lung neoplasm ([@ref-1]; [@ref-17]). However, currently no research compares the two operations, wedge resection and segmental resection, which constitute the sublobectomy, in TC patients. Although both surgeries are sublobectomies, wedge resection causes a smaller operative wound than segmental resection.

Now that surgery is the main choice of treatment for TC patients, and given that other therapeutic methods are not powerful, the smaller operative wound is a major consideration after guaranteeing the survival rate. The objective of this research is to determine if there is a difference between wedge resection and segmental resection for early stage TC patients.

Materials & Methods
===================

Data source
-----------

We have been given access to the SEER databases in October 2018 with the "numbered" SEER\*Stat account(12991-Nov2017). The retrospective research collected the data from the Surveillance, Epidemiology and End Results (SEER) by using SEER\*Stat 8.3.5 in December 2018. The inclusion criteria were as follows: (I) TC patients (code 8240) at the localized stage; (II) patients treated via no surgery at the primary site (code 00), wedge resection (code 21), segmentectomy (code 22), or lobectomy (code 33); (III) patients with only one primary tumor. The exclusion criteria included: (I) diagnosis before 2004, (II) survival of less than one month or unknown, (III) lung cancer-special survival (LCSS) missing, (IV) tumor size unknown, (V) scope of regional lymph node surgery unknown, (VI) radiation therapy unknown, and (VII) regional, distant, or unknown summary stage.

Variates
--------

Demographic information for patients included patient ID, age, gender, and race. Age at diagnosis was divided into two groups, under 70 and 70 or older. Race was categorized into white and other. Variables collected for the research included pathological data, treatment, and follow-up information, such as laterality, surgery, procedure used, tumor size, scope of regional lymph node surgery, radiation, chemotherapy, summary stage, differentiation grade, overall survival status, LCSS, and survival month.

Statistical analyses
--------------------

Unbalanced distribution of variables between groups was evaluated by chi-square test. A KM curve was generated to assess survival and a log-rank test was used to evaluate survival discrepancy. Univariate and multivariate Cox proportional hazards regressions were conducted to evaluate the effects of involved factors on prognosis, acquire hazards ratio, and generate a 95% confidence interval (HR and 95% CI). Propensity score matching (PSM) of 1:1 was used to eliminate the differences of variable components between wedge and segmental resection, and the caliper was 0.01. Statistical analysis was performed with SPSS 24.0 software (SPSS Inc, Chicago, IL). Significance was set at *P* of less than 0.05.

Result
======

Prognosis for carcinoid, squamous cell cancer (SCC), and adenocarcinoma (ADC) in lung
-------------------------------------------------------------------------------------

Presently squamous cell cancer and adenocarcinoma are common forms of lung cancer, accounting for 78% of this disease. Lung carcinoid is composed of typical carcinoid and atypical carcinoid. To acquire general prognosis information about TC patients, we compared the cumulative survival rate for lung carcinoid and its components with SCC and ADC. The clinical information was recorded in [Table 1](#table-1){ref-type="table"}. Obviously, carcinoid has the more favorable prognosis compared with SCC and ADC in overall survival (OS) and lung cancer-specific survival (LCSS) ([Fig. 1](#fig-1){ref-type="fig"}), as follows: hazard ratio (HR) = 0.149 (0.141--0.519), *P* \< 0.001 of carcinoid versus ADC in OS; HR = 0.092 (0.085--0.100), *P* \< 0.001 of carcinoid versus ADC in LCSS; HR=1.192 (1.181--1.204), *P* \< 0.001 of SCC versus ADC in OS; HR = 1.135 (1.123--1.147), *P* \< 0.001 of SCC versus ADC in LCSS.

10.7717/peerj.7519/table-1

###### Baseline Information for comparison among Adenocarcinoma, SCC and Carcinoid.

![](peerj-07-7519-g007)

                                       Adenocarcinoma   SCC      Carcinoid   AC      TC      
  ------------------------------------ ---------------- -------- ----------- ------- ------- --
  Race                                                                                       
  White                                133,061          66,319   4,666       4,183   483     
  Black                                19,659           10,057   381         344     37      
  Others                               15,546           4,311    197         19      178     
  Gender                                                                                     
  Female                               87,558           29,751   3,574       350     3,224   
  Male                                 80,708           50,936   1,670       189     1,481   
  Primary Site                                                                               
  Main Bronchus                        4,914            5,190    286         30      256     
  Upper Lobe                           84,247           42,587   1,540       171     1,369   
  Middle Lobe                          8,221            2,833    897         88      809     
  Lower Lobe                           44,029           22,265   2,117       201     1,916   
  Others                               26,855           7,812    404         49      355     
  Laterality                                                                                 
  Left                                 63,614           33,873   2,065       215     1,850   
  Right                                95,605           44,602   3,069       314     2,755   
  Others                               9,047            2,212    110         10      100     
  Grade                                                                                      
  I                                    15,316           1,642    1,767       60      1,707   
  II                                   32,248           21,232   488         175     313     
  III                                  39,710           27,415   39          11      28      
  IV                                   1,457            574      15          5       10      
  Others                               79,535           29,824   2,935       288     2,647   
  TNM Stage                                                                                  
  I                                    33,843           17,665   1,936       240     1,696   
  II                                   6,339            5,573    400         56      344     
  III                                  34,607           24,946   301         112     189     
  IV                                   80,900           27,311   338         104     234     
  Others                               12,577           5,192    2,269       27      2,242   
  T                                                                                          
  0                                    895              189      0           0       0       
  1                                    34,263           11,815   1,703       217     1,486   
  2                                    42,925           27,268   724         172     552     
  3                                    6,797            7,486    268         13      255     
  4                                    61,538           26,729   259         99      160     
  Others                               21,848           7,200    2,290       38      2,252   
  N                                                                                          
  0                                    63,527           31,446   2,504       303     2,201   
  1                                    13,234           7,844    247         72      175     
  2                                    53,635           28,058   264         126     138     
  3                                    20,096           8,247    38          15      23      
  Others                               17,774           5,092    2,191       23      2,168   
  M                                                                                          
  0                                    77,237           50,072   2,785       418     2,367   
  1                                    80,900           27,311   338         104     234     
  Others                               10,129           3,304    2,121       17      2,104   
  Summary Stage                                                                              
  Localized                            31,653           15,415   3,346       225     3,121   
  Regional                             33,274           25,968   1,072       178     894     
  Distant                              99,878           37,202   675         119     556     
  Others                               3,461            2,102    151         17      134     
  Surgery                                                                                    
  No                                   120,379          61,452   1,052       127     925     
  Sublobar Resection                   9,597            3,116    1,128       95      1,033   
  Lobectomy/Bilobectomy                35,236           12,992   2,790       280     2,510   
  Pneumonectomy                        1,559            2,008    186         29      157     
  Others                               1,495            1,119    88          8       80      
  Chemotherapy                                                                               
  No/Unknown                           93,973           46,482   4,953       406     4,547   
  Yes                                  74,293           34,205   291         133     158     
  Radiotherapy                                                                               
  No/Unknown                           109,686          43,866   4,973       458     4,515   
  Yes                                  58,580           36,821   271         81      190     
  Overall Survival Rate                                                                      
  3-year Survival (%)                  30.81            22.67    87.88       73.28   89.38   
  5-year Survival (%)                  22.78            16.01    83.03       64.50   84.84   
  10-year Survival (%)                 14.81            8.56     72.43       44.30   74.49   
  Lung Cancer Specific Survival Rate                                                         
  3-year Survival (%)                  34.29            27.55    92.03       76.70   93.60   
  5-year Survival (%)                  27.01            21.92    89.89       67.84   92.01   
  10-year Survival (%)                 21.16            17.01    85.70       48.14   88.45   

**Notes.**

SCCSquamous lung carcinomaACAtypical CarcinoidTCTypical Carcinoid

![OS and LCSS for ADC, SCC and carcinoid patients evaluated using KM plots.\
Overall survival and lung cancer-special survival among adenocarcinoma, squamous lung cancer and carcinoid (A, C). Overall survival and Lung cancer-special survival among adenocarcinoma, squamous lung cancer, typical carcinoid and atypical carcinoid (B, D). HR is from Cox regression analysis. *P* value is from a log-rank test. HR, hazard ratio; OS, overall survival; LCSS, Lung cancer-special survival.](peerj-07-7519-g001){#fig-1}

Furthermore, TC has a better prognosis than AT in OS and LCSS, as follows: HR = 2.105 (1.786--2.480), *P* \< 0.001 of AT versus TC in OS; HR=3.768 (3.122--4.549), *P* \< 0.001 of AT versus TC in LCSS.

In conclusion, typical carcinoid has a more favorable prognosis than the other three types of lung cancers.

Baseline information of TC patients from SEER database
------------------------------------------------------

There were 1,887 TC patients in our cohort: 235 patients with no surgery, 465 undergoing wedge resection, 113 receiving segmental resection, and 1,074 going under the lobectomy. Some demographic and clinical information, such as age, gender, race, etc., was been recorded ([Table 2](#table-2){ref-type="table"}). Notably, 71.8% patients were female and most patients were white. Compared with the no surgery group, the percentages of old patients (age ≥ 70 years) are less than 30% of the other three surgery groups: 58.3% in no surgery, 27.1% in wedge resection, 15.9% in segmental resection, and 18.1% in lobectomy. Thus, it can be seen that age may be an important factor in choosing a treatment option. In addition, the number of female patients is much larger than that of male patients no matter what treatment they receive. As for the factor "scope of the lymph node," wedge resection results in less regional lymph node resection compared to segmental resection or lobectomy: the percentage of no regional lymph node resection is 68.6% in wedge resection and 38.9% in segmental resection.

10.7717/peerj.7519/table-2

###### Baseline characteristics of all TC patients.

![](peerj-07-7519-g008)

  Characteristic                 No surgery    Wedge         Segmental     Lobectomy      Total
  ------------------------------ ------------- ------------- ------------- -------------- --------------
  Age                                                                                     
  \<70y                          98 (41.7%)    339 (72.9%)   95 (84.1%)    880 (81.9%)    1412 (74.8%)
  ≥70y                           137 (58.3%)   126 (27.1%)   18 (15.9%)    194 (18.1%)    475 (25.2%)
  Gender                                                                                  
  Female                         172 (73.2%)   355 (76.3%)   80 (70.8%)    738 (68.7%)    1345 (71.3%)
  Male                           63 (26.8%)    110 (23.7%)   33 (29.2%)    336 (31.3%)    542 (28.7%)
  Race                                                                                    
  White                          201 (85.5%)   419 (90.1%)   102 (90.3%)   979 (91.2%)    1701 (90.1%)
  Black                          25 (10.6%)    27 (5.8%)     8 (7.1%)      54 (5.0%)      114 (6.0%)
  Others                         9 (3.9%)      19 (4.1%)     3 (2.6%)      41 (3.8%)      72 (3.9%)
  Grade                                                                                   
  Well/Moderate                  76 (32.3%)    194 (41.7%)   52 (46.0%)    571 (53.2%)    893 (47.3%)
  Poor/Undifferentiated          1 (0.4%)      3 (0.6%)      1 (0.9%)      3 (0.3%)       8 (0.4%)
  Unknown                        158 (67.3%)   268 (57.7%)   60 (53.1%)    500 (46.5%)    986 (52.3%)
  Laterality                                                                              
  Right                          146 (62.1%)   261 (56.1%)   43 (38.1%)    648 (60.3%)    1098 (58.2%)
  Left                           89 (37.9%)    204 (43.9%)   70 (61.9%)    426 (39.7%)    789 (41.8%)
  Tumor size                                                                              
  T1 (≤3 cm)                     184 (78.3%)   453 (97.4%)   105 (92.9%)   904 (84.2%)    1646 (87.2%)
  T2 (≤5 cm, \<3 cm)             38 (16.2%)    11 (2.4%)     7 (6.2%)      138 (12.8%)    194 (10.3%)
  T3 (≤7 cm, \>5 cm)             6 (2.5%)      -- --         1 (0.9%)      20 (1.9%)      27 (1.4%)
  T4 (\>7 cm)                    7 (3.0%)      1 (0.2%)      -- --         12 (1.1%)      20 (1.1%)
  Scope of regional lymph node                                                            
  0                              235 (100%)    319 (68.6%)   44 (38.9%)    4 (0.4%)       602 (31.9%)
  1--3                           -- --         88 (18.9%)    29 (25.7%)    166 (15.5%)    283 (15.0%)
  \>3                            -- --         58 (12.5%)    40 (35.4%)    904 (84.1%)    1002 (53.1%)
  Radiation                                                                               
  No                             209 (89.9%)   462 (99.4%)   112 (99.1%)   1068 (99.4%)   1851 (98.1%)
  Yes                            26 (11.1%)    3 (0.6%)      1 (0.9%)      6 (0.6%)       36 (1.9%)
  Chemotherapy                                                                            
  No                             232 (98.7%)   464 (99.8%)   112 (99.1%)   1068 (99.4%)   1876 (99.4%)
  Yes                            3 (1.3%)      1 (0.2%)      1 (0.9%)      6 (0.6%)       11 (0.6%)

Prognosis for TC patients treated with no surgery, wedge resection, segmental resection, and lobectomy
------------------------------------------------------------------------------------------------------

The influence of surgery and surgery type on overall survival (OS) and lung cancer-specific survival (LCSS) for pulmonary TC patients were evaluated using KM curves ([Figs. 2A](#fig-2){ref-type="fig"}, [2D](#fig-2){ref-type="fig"}). There were significant differences between the group with no surgery and the other three groups, both in OS and LCSS: The 5-year survival rate of the no surgery, wedge resection, segmental resection, and lobectomy, respectively, were 73%, 90%, 94%, and 94% for OS (*P* \< 0.001). There is an even greater gap between patients with no surgery and groups who underwent surgery when the 10-year survival rate is examined.

![OS and LCSS for pulmonary TC patients evaluated using KM plots.\
Overall survival (A) and lung cancer-special survival (D) among no surgery (*n* = 235), wedge resection (*n* = 465), segmental resection (*n* = 113) and lobectomy (*n* = 1,074) TC patients at localized stage form SEER project. Overall survival (B) and lung cancer specific survival (E) in wedge resection versus lobectomy after PSM. Overall survival (C) and lung cancer specific survival (F) in wedge resection versus segmental resection after PSM. The difference of OS between two operations was eliminated after PSM: *P* = 0.256. *P* value is from a log-rank test. OS, overall survival; LCSS, Lung cancer-special survival; No., no surgery; Wed., wedge resection; Seg., segmental resection; Lob., lobectomy.](peerj-07-7519-g002){#fig-2}

For further research about the impact of surgery type, the three groups were defined here as pairs to be assessed with KM curves ([Fig. 3](#fig-3){ref-type="fig"}). Although the comparison between lobectomy and wedge resection indicated that the difference in patient prognoses was statistically significant for OS (*P* \< 0.001), the propensity score match (PSM) eliminated this diversity between those groups for OS (*P* = 0.256) ([Figs. 2B](#fig-2){ref-type="fig"}, [2E](#fig-2){ref-type="fig"}). The results of other contrast groups showed comparable prognoses for both OS and LCSS (*P* \> 0.05).

![Three surgery groups were assessed as pairs with KM curves.\
Overall survival and lung cancer specific survival in wedge resection versus lobectomy, segmental resection versus lobectomy, wedge resection versus segmental resection. There was no significant difference between two surgical options in OS except wedge versus lobectomy: (A) wedge resection versus lobectomy, *P* \< 0.001; (B) segmental resection versus lobectomy, *P* = 0.150; (C) wedge resection versus segmental resection, *P* = 0.492. There was no significant difference between two surgical options in LCSS: (D) wedge resection versus lobectomy, *P* = 0.983; (E) segmental resection versus lobectomy, *P* = 0.882; (F) wedge resection versus segmental resection, *P* = 0.912. OS, overall survival; LCSS, Lung cancer-special survival; No., no surgery; Wed., wedge resection; Seg., segmental resection; Lob., lobectomy.](peerj-07-7519-g003){#fig-3}

Univariate and multivariate COX regression analyses of TC patients in the localized stage
-----------------------------------------------------------------------------------------

Relative risk factors for OS were analyzed using univariate and multivariate COX regression hazard models ([Table 3](#table-3){ref-type="table"}). The factors whose *P* \< 0.05, both in univariate and multivariate analysis, are: age (*P* \< 0.001 in multivariate analysis), gender (*P* = 0.037 in multivariate analysis), and surgery (*P* \< 0.001 in multivariate analysis). For OS, age, gender, and surgery were independent prognostic factors with HR as follows: 3.889 (95% CI \[2.536--5.965\], ≥70 y versus \<70 y), 1.574 (95% CI \[1.028--2.410\], female versus male), 0.520 (95% CI \[0.317--0.853\], wedge resection versus no surgery, *P* = 0.008), 0.259 (95%CI \[0.095--0.706\], segmental resection versus no surgery, *P* \< 0.001), 0.159 (95% CI \[0.059--0.427\], lobectomy versus no surgery, *P* \< 0.001).

10.7717/peerj.7519/table-3

###### Univariate and multivariate Cox regression analyses according to OS for TC patients.

![](peerj-07-7519-g009)

  Variables in the equation      Univariate                                  Multivariate                                                        
  ------------------------------ ------------------------------------------- ----------------------- ------------------------------------------- -----------------------
  Age                                                                                                                                            
  \<70y                          --                                          --                      --                                          --
  ≥70y                           [^\*^](#table-3fn1){ref-type="fn"}\<0.001   4.553 (3.358--6.173)    [^\*^](#table-3fn1){ref-type="fn"}\<0.001   3.889 (2.536--5.965)
  Gender                                                                                                                                         
  Female                         --                                          --                      --                                          --
  Male                           0.008                                       1.521 (1.116--2.073)    0.037                                       1.574 (1.028--2.410)
  Race                                                                                                                                           
  White                          0.050                                       --                      0.056                                       --
  Black                          0.033                                       1.753 (1.047--2.936)    0.056                                       2.058 (0.980--4.321)
  Others                         0.272                                       0.527 (0.168--1.652)    0.166                                       0.247 (0.034--1.782)
  Grade                                                                                                                                          
  Well/Moderate                  [^\*^](#table-3fn1){ref-type="fn"}\<0.001   --                      0.176                                       --
  Poor/Undifferentiated          0.011                                       6.285 (1.522--25.950)   0.063                                       3.992 (0.930--17.137)
  Unknown                        [^\*^](#table-3fn1){ref-type="fn"}\<0.001   2.172 (1.449--3.255)    0.902                                       1.035 (0.600--1.785)
  Laterality                                                                                                                                     
  Right                          --                                          --                      --                                          --
  Left                           0.908                                       0.982 (0.724--1.333)    --                                          --
  Tumor size                                                                                                                                     
  T1 (≤1 cm)                     0.112                                       --                      --                                          --
  T2 (≤2 cm, \>1 cm)             0.309                                       0.811 (0.543--1.213)    --                                          --
  T3 (≤3 cm, \>2 cm)             0.092                                       0.660 (0.407--1.070)    --                                          --
  T4 (\>3cm)                     0.533                                       1.168 (0.717--1.902)    --                                          --
  Scope of regional lymph node                                                                                                                   
  *n* = 0                        [^\*^](#table-3fn1){ref-type="fn"}\<0.001   --                      0.357                                       --
  *n* \> 0, *n* ≤ 3              [^\*^](#table-3fn1){ref-type="fn"}\<0.001   0.346 (0.212--0.566)    0.960                                       0.974 (0.357--2.659)
  *n* \> 3                       [^\*^](#table-3fn1){ref-type="fn"}\<0.001   0.305 (0.217--0.428)    0.225                                       1.763 (0.706--4.403)
  Surgery                                                                                                                                        
  No surgery                     [^\*^](#table-3fn1){ref-type="fn"}\<0.001   --                      0.001                                       --
  Wedge resection                [^\*^](#table-3fn1){ref-type="fn"}\<0.001   0.281 (0.192--0.412)    0.008                                       0.520 (0.317--0.853)
  Segmental resection            [^\*^](#table-3fn1){ref-type="fn"}\<0.001   0.228 (0.117--0.444)    [^\*^](#table-3fn1){ref-type="fn"}\<0.001   0.259 (0.095--0.706)
  Lobectomy                      [^\*^](#table-3fn1){ref-type="fn"}\<0.001   0.140 (0.097--0.202)    [^\*^](#table-3fn1){ref-type="fn"}\<0.001   0.159 (0.059--0.427)

**Notes.**

*p* \< 0.05, statistically significant.

The hazard study for LCSS was completed in the same way ([Table 4](#table-4){ref-type="table"}). Data showed that age (*P* = 0.008 in multivariate analysis), tumor size (*P* = 0.012 in multivariate analysis), and surgery (*P* = 0.004 in multivariate analysis) are independent prognostic factors whose *P* \< 0.05 both in univariate and multivariate analysis. As for LCSS, the HR of independent prognostic factors is as follows: 2.261 (95% CI \[1.232--4.149\], ≥70 y versus \<70 y), 0.167 (95%CI \[0.061--0.461\], wedge resection versus no surgery, *P* = 0.001), 0.197 (95% CI \[0.040--0.967\], segmental resection versus no surgery, *P* = 0.045), 0.158 (95% CI \[0.026--0.951\], lobectomy versus no surgery, *P* = 0.044). The independent prognostic factors for both OS and LCSS were age and surgery.

10.7717/peerj.7519/table-4

###### Univariate and multivariate Cox regression analyses according to LCSS for TC patients.

![](peerj-07-7519-g010)

  Variables in the equation      Univariate                                  Multivariate                                                      
  ------------------------------ ------------------------------------------- ----------------------- ----------------------------------------- ----------------------
  Age                                                                                                                                          
  \<70y                          --                                          --                      --                                        --
  ≥70y                           [^\*^](#table-4fn1){ref-type="fn"}\<0.001   4.112 (2.341--7.225)    [^\*^](#table-4fn1){ref-type="fn"}0.008   2.261 (1.232--4.149)
  Gender                                                                                                                                       
  Female                         --                                          --                      --                                        --
  Male                           0.362                                       1.315 (0.730--2.368)    --                                        --
  Race                                                                                                                                         
  White                          0.348                                       --                      --                                        --
  Black                          0.151                                       1.753 (1.047--2.936)    --                                        --
  Others                         0.755                                       0.527 (0.168--1.652)    --                                        --
  Grade                                                                                                                                        
  Well/Moderate                  0.086                                       --                      --                                        --
  Poor/Undifferentiated          [^\*^](#table-4fn1){ref-type="fn"}0.027     9.928 (1.301--75.743)   --                                        --
  Unknown                        0.756                                       1.143 (0.492--2.655)    --                                        --
  Laterality                                                                                                                                   
  Right                          --                                          --                      --                                        --
  Left                           0.641                                       1.143 (0.651--2.007)    --                                        --
  Tumor size                                                                                                                                   
  T1 (≤1 cm)                     [^\*^](#table-4fn1){ref-type="fn"}\<0.001   --                      [^\*^](#table-4fn1){ref-type="fn"}0.012   --
  T2 (≤2 cm, \>1 cm)             0.924                                       0.955 (0.371--2.463)    0.663                                     0.806 (0.305--2.127)
  T3 (≤3 cm, \>2 cm)             0.536                                       1.369 (0.506--3.703)    0.670                                     1.255 (0.441--3.574)
  T4 (\>3 cm)                    [^\*^](#table-4fn1){ref-type="fn"}0.005     3.853 (1.519--9.774)    [^\*^](#table-4fn1){ref-type="fn"}0.060   2.586 (0.960--6.968)
  Scope of regional lymph node                                                                                                                 
  *n* = 0                        [^\*^](#table-4fn1){ref-type="fn"}\<0.001   --                      0.357                                     --
  *n* \> 0, *n* ≤ 3              [^\*^](#table-4fn1){ref-type="fn"}0.003     0.169(0.052--0.552)     0.960                                     0.974 (0.357--2.659)
  *n* \> 3                       [^\*^](#table-4fn1){ref-type="fn"}\<0.001   0.244(0.129--0.465)     0.225                                     1.763 (0.706--4.403)
  Surgery                                                                                                                                      
  No surgery                     [^\*^](#table-4fn1){ref-type="fn"}\<0.001   --                      [^\*^](#table-4fn1){ref-type="fn"}0.004   --
  Wedge resection                [^\*^](#table-4fn1){ref-type="fn"}\<0.001   0.089(0.037--0.216)     [^\*^](#table-4fn1){ref-type="fn"}0.001   0.167 (0.061--0.461)
  Segmental resection            [^\*^](#table-4fn1){ref-type="fn"}0.002     0.106(0.025--0.448)     [^\*^](#table-4fn1){ref-type="fn"}0.045   0.197 (0.040--0.967)
  Lobectomy                      [^\*^](#table-4fn1){ref-type="fn"}\<0.001   0.089(0.047--0.170)     [^\*^](#table-4fn1){ref-type="fn"}0.044   0.158 (0.026--0.951)

**Notes.**

*p* \< 0.05, statistically significant.

Prognosis of TC patients who underwent wedge resection or segmental resection before and after PSM
--------------------------------------------------------------------------------------------------

According to the selection criterion, 465 patients in the cohort received wedge resection and 113 underwent segmental resection. A distinctly unequal distribution of factors existed between these two groups ([Table 5](#table-5){ref-type="table"}). To reach a more objective conclusion, factors such as age, laterality, tumor size, and scope of regional lymph node must be balanced. Compared with wedge resection, segmental resection was more often offered to people of older age, with larger tumor sizes, who had a larger region of lymph node resected.

10.7717/peerj.7519/table-5

###### Baseline characteristics for patients whom underwent wedge resection/segmentectomy before and after PSM.

![](peerj-07-7519-g011)

  Characteristic                 Before PSM         After PSM                                              
  ------------------------------ ------------ ----- ------------------------------------------- ----- ---- -------
  Age                                               [^\*^](#table-5fn1){ref-type="fn"}0.015                1.000
  \<70y                          339          95                                                83    82   
  ≥70y                           126          18                                                17    18   
  Gender                                            0.226                                                  0.629
  Female                         355          80                                                76    72   
  Male                           110          33                                                24    28   
  Race                                              1.000                                                  0.822
  White                          419          102                                               88    90   
  Others                         46           11                                                12    10   
  Grade                                             0.611                                                  0.352
  Well/Moderate                  172          45                                                41    39   
  Poor/Undifferentiated          25           8                                                 2     6    
  Unknown                        268          60                                                57    55   
  Laterality                                        [^\*^](#table-5fn1){ref-type="fn"}0.001                1.000
  Right                          261          43                                                42    41   
  Left                           204          70                                                58    59   
  Tumor size                                        [^\*^](#table-5fn1){ref-type="fn"}\<0.001              0.251
  T1 (≤1 cm)                     159          30                                                41    30   
  T2 (≤2 cm, \>1 cm)             253          50                                                38    43   
  T3 (\>2 cm)                    53           33                                                21    27   
  Scope of regional lymph node                      [^\*^](#table-5fn1){ref-type="fn"}\<0.001              0.845
  0                              319          44                                                37    41   
  1--3                           88           29                                                31    29   
  \>3                            58           40                                                32    30   
  Radiation                                         0.058                                                  1.000
  No                             462          112                                               100   99   
  Yes                            3            1                                                 0     1    
  Chemotherapy                                      0.353                                                  1.000
  No                             464          112                                               100   99   
  Yes                            1            1                                                 0     1    

**Notes.**

*p* \< 0.05, statistically significant.

To avoid being influenced by factors' disproportionate distribution and data bias, we used PSM (an analysis function of the software, Statistical Package for the Social Sciences) to acquire an adequate sample set. First, we found the unbalanced variates by *t*-test. Then we chose the PSM to solve those imbalances by matching analogical cases from two groups. After 1:1 PSM, 100 patients who underwent wedge resection and 100 patients with segmental resection were involved in the final research. Meanwhile, all factors, including age, laterality, tumor size, were balanced to some extent ([Table 5](#table-5){ref-type="table"}).

10.7717/peerj.7519/table-6

###### Univariate Cox regression analyses according to OS and LCSS for TC patients whom underwent wedge and segmental resection.

![](peerj-07-7519-g012)

  Variables in the equation      OS                                          LCSS                             
  ------------------------------ ------------------------------------------- ---------------------- --------- -----------------------
  Age                                                                                                         
  \<70y                          --                                          --                     --        --
  ≤70y                           [^\*^](#table-6fn1){ref-type="fn"}\<0.001   4.141 (2.430--7.058)   \*0.021   5.428 (1.296-22.728)
  Gender                                                                                                      
  Male                           --                                          --                     --        --
  Female                         0.093                                       1.612 (0.924--2.812)   0.915     1.092 (0.220--5.430)
  Race                                                                                                        
  White                          --                                          --                     --        --
  Others                         0.581                                       0.751 (0.271--2.077)   0.575     0.331 (0.007--15.723)
  Grade                                                                                                       
  Well/Moderate                  0.872                                       --                     0.681     --
  Poor/Undifferentiated          0.604                                       0.676 (0.154--2.963)   0.488     2.350 (0.210--26.312)
  Unknown                        0.830                                       0.935 (0.508--1.722)   0.902     0.899 (0.167--4.847)
  Laterality                                                                                                  
  Right                          --                                          --                     --        --
  Left                           0.812                                       1.066 (0.628--1.810)   0.143     3.311 (0.668--16.417)
  Tumor size                                                                                                  
  T1 (≤1 cm)                     0.456                                       --                     0.682     --
  T2 (≥2 cm, \>1 cm)             0.377                                       0.776 (0.443-1.361)    0.653     0.693 (0.140--3.438)
  T3 (≤2 cm)                     0.258                                       0.595 (0.242--1.463)   0.638     1.537 (0.257--9.202)
  Scope of regional lymph node                                                                                
  *n* ≤ 3                        --                                          --                     --        --
  *n* \> 3                       0.698                                       0.845 (0.361--1.979)   0.297     2.366 (0.470--11.917)
  Surgery                                                                                                     
  Wedge resection                --                                          --                     --        --
  Segmental resection            0.493                                       0.786 (0.395--1.564)   0.912     1.096 (0.217--5.541)

**Notes.**

*p* \< 0.05, statistically significant.

The prognoses for 100 pairs of patients after exactly matching were evaluated using KM curves ([Figs. 2C](#fig-2){ref-type="fig"}, [2F](#fig-2){ref-type="fig"}). The difference between wedge resection and segmental resection did not achieve statistical significance: for OS, the 5-year survival rates of wedge resection and segmental resection were 90.07% and 94.17% respectively, and the 10-year survival rates of wedge resection and segmental resection were 83.48% and 84.78%, respectively (*P* = 0.320); for LCSS, the 5-year survival rates of wedge resection and segmental resection were 97.89% and 98.75%, respectively, and the 10-year survival rates of wedge resection and segmental resection were 93.67% and 98.75%, respectively (*P* = 0.342).

Univariate COX regression analyses of TC patients who underwent wedge resection and segmental resection before PSM
------------------------------------------------------------------------------------------------------------------

Relative risk factors for OS and LCSS were analyzed using a univariate COX regression hazard model ([Table 6](#table-6){ref-type="table"}). The study showed that age was only a prognostic factor for OS and LCSS: HR = 4.141 (95% CI \[2.430--7.058\], *P* \< 0.001) for OS, and HR = 5.428 (95% CI \[1.296--22.728\], *P* = 0.021) for LCSS. Notably, gender (*P* = 0.093) and tumor size (*P* = 0.682) no longer independently affected the prognoses for OS and LCSS, respectively.

Subgroup analysis of TC patients who received wedge or segmental resection for OS and LCSS before PSM
-----------------------------------------------------------------------------------------------------

The results showed no statistically significant difference between wedge and segmental resection in any subgroup of age, race, gender, tumor size, or scope of regional lymph node, which was rendered in KM plots ([Figs. 4](#fig-4){ref-type="fig"}--[6](#fig-6){ref-type="fig"}). Cox regression analysis for OS also supported that view ([Table 7](#table-7){ref-type="table"}). The results of Cox regression analysis for LCSS are not shown because death was rare after sectionalization.

![Prognostic analysis for subgroup of age and sex by KM plots.\
Overall survival and lung cancer specific survival in subgroups of age (\<70 and ≥70) and gender (female and male) between wedge resection and segmental resection. There was no significant difference between two surgical options in OS: (A) age \< 70; (B) age ≥ 70; (C) female; (D) male. Besides, there was no significant difference between two surgical options in LCSS: (E) age \< 70; (F) age ≥ 70; (G) female; (H) male. OS, overall survival; LCSS, Lung cancer-special survival.](peerj-07-7519-g004){#fig-4}

![Prognostic analysis for subgroup of race and Scope of Regional Lymph Node by KM plots.\
Overall survival and lung cancer specific survival in subgroups of race (white and others) and Scope of regional Lymph node (0--3 and ≥3) between wedge resection and segmental resection. There was no significant difference between two surgical options in OS: (A) white; (B) others; (C) 0--3; (D) ≥3. Besides, there was no significant difference between two surgical options in LCSS: (E) white; (F) 0--3; (G) ≥3. No death case was found in Others (subgroup of race) in LCSS so that the KM curves was missing. OS, overall survival; LCSS, Lung cancer-special survival; Scope of Reg. LN Sur., Scope of Regional Lymph Node.](peerj-07-7519-g005){#fig-5}

![Prognostic analysis for subgroup of tumor siza by KM plots.\
Overall survival and lung cancer specific survival in subgroups of tumor size (size ≤1 cm, 1 cm 2 cm) between wedger resection and segmental resection. There was no significant difference between two surgical options in OS: (A) size ≤ 1 cm; (B) size \>1 cm and size ≤2 cm; (C) size \> 2 cm. Similarly, there was no significant difference between two surgical options in LCSS: (D) size ≤ 1 cm; (E) size \>1 cm and size ≤ 2 cm; (F) size \> 2 cm. OS, overall survival; LCSS, Lung cancer-special survival.](peerj-07-7519-g006){#fig-6}

10.7717/peerj.7519/table-7

###### Subgroup analyses according to OS and LCSS before PSM.

![](peerj-07-7519-g013)

  Variables in the equation      OS      
  ------------------------------ ------- -----------------------
  Age                                    
  \<70y                          0.220   0.469 (0.140--1.574)
  ≥70y                           0.393   1.448 (0.619--3.384)
  Gender                                 
  Female                         0.451   0.712 (0.295--1.721)
  Male                           0.914   0.941 (0.312--2.837)
  Race                                   
  White                          0.373   0.719 (0.348--1.485)
  Others                         0.686   1.601 (0.163--15.704)
  Tumor size                             
  T1 (≤1 cm)                     0.696   0.804 (0.269--2.403)
  T2 (≤2 cm, \>1 cm)             0.249   0.428 (0.101--1.811)
  T3 (≥2 cm)                     0.254   2.706 (0.489--14.969)
  Scope of regional lymph node           
  *n* ≤ 3                        0.692   0.857 (0.400--1.837)
  *n* \> 3                       0.546   0.592 (0.108--3.245)

Discussion
==========

The study showed that the prognosis of TC patients was best among those suffering from ADC and SCC. Further univariate and multivariate Cox analysis showed that the surgery option was independent of the prognosis for OS and LCSS in TC patients. As for the impact of surgery type (wedge and segmental resection) on survival, the result was not statistically significant either before or after PSM. In conclusion, the important discovery of this report is that wedge resection is likely to be equal to segmental resection for TC patients at the localized stage.

As the low-grade lung NET, TC has a favorable prognosis, where the 5-year and 10-year survival rate for OS and LCSS were highest compared with NSCLC and AC ([Table 1](#table-1){ref-type="table"}). Some studies also showed that 5-year OS of TC was more than 87 percent ([@ref-6]; [@ref-10]). The excellent prognosis for TC may be attributed to a handful of mitoses, no necrosis, and a low Ki-67 labeling index ([@ref-2]; [@ref-16]). However, other research has indicated that the survival rate for Pulmonary carcinoids (PCs) has dropped for the past 30 years ([@ref-9]). In its milder forms, it may still be a major problem increasing mortality and delaying diagnosis. Compared with other lung carcinomas, only 10.4% of primary TC is located in the bronchi, so respiratory symptoms, such as chest infections, cough, hemoptysis, and chest pain are relatively rare ([@ref-9]; [@ref-2]). Similarly, lung neoplasms were larger than five cm resected from the TC patients at the localized stage because the symptoms were so mild.

For TC patients who were at the localized stage, age, gender, and surgery option were independent prognostic factors for OS in the multivariate Cox analysis. However, the factor "gender" was replaced by the factor "tumor size" in assessment for LCSS in the multivariate analysis. Same with James W. Vaupel 's finding, Women live longer than men today ([@ref-19]). Long life span of female may contribute to the cause differences in analysis of OS. Besides, unlike OS, people were classified as having died from LCSS only when the cause was related to lung cancer. Therefore, gender may not influence the progress of death from TC. The significant difference between the group with no surgery and the group who underwent surgery indicated that surgery was essential for the treatment of TC even though it had low malignancy. In a Cox regression model with time dependence, age was statistically significant (data not shown). The HR increases as patients age.

Like the results of Taher Abu Hejleh et al. ([@ref-8]), research on surgery type showed that TC patients at the localized stage would benefit equally from lobectomy or sublobectomy. However, Taher Abu Hejleh et al. overlooked that sublobectomy contained both wedge and segmental resection. Comparisons between sublobectomy and lobectomy respectively were not done. Thus, superiority of lobectomy cannot be proved by being contrasted with sublobectomy, similar anatomy resection (segmentectomy), or wedge resection.

The emphasis of this research is on whether the benefits of wedge resection can equal those of segmentectomy. The raw data indicated that the choice between the two procedures did not influence the prognosis of patients who underwent sublobectomy. Furthermore, after 1:1 PSM, the gaps between the OS and LCSS survival rate of two surgery procedures closed, providing additional evidence for the uniformity of the benefits from treatment, whether treatment consisted of wedge resection or segmentectomy produced in TC therapy. Besides, the Cox analysis of TC patients who underwent those two surgeries before PSM showed that only age was a relevant prognostic factor for OS or LCSS, and surgery type was no exception. The therapeutic effect of sublobectomy eliminated the impact of factors other than age on prognosis and both two operating methods were effective for TC. Furthermore, this held true for many subgroups of TC patients, including groups that were younger or older, or male or female, verified by the subgroup analyses.

A survey that involved 172 institutions worldwide showed that only 11 percent of participants regarded wedge resection as an appropriate surgical option for peripheral PCs ([@ref-2]). However, the results of this research showed that patients did not benefit more from segmental resection than wedge resection. Compared to the anatomic resection, the operation wound from wedge resection was milder and caused less damage to pulmonary function. Therefore, the results proved that wedge resection, as well as anatomic resection, should be considered a conventional treatment for TC patients at the localized stage. Preserving better pulmonary function and leaving a smaller surgical wound will promote better quality of life for patients undergoing the surgery.

Inevitably, there are several limitations similar to those of most retrospective studies based on the SEER database used for this study. First of all, information on patients, such as complications, recurrence, follow-up treatment received, TMN stage, and so on was not complete. This reduced the level of accuracy and detail of the prognoses. Secondly, the number of cases was limited because the disease is rare. The results of the research will be more convincing when additional cases are studied. Third, this research may include more bias than a prospective study or a randomized trial.

Conclusion
==========

The wedge resection was a comparable treatment to segmental resection for TC patients at the localized stage.

Supplemental Information
========================

10.7717/peerj.7519/supp-1

###### Raw data for 1887 TC patients

###### 

Click here for additional data file.

10.7717/peerj.7519/supp-2

###### Raw data for SCC TC AT patients in [Table 1](#table-1){ref-type="table"} and [Fig. 1](#fig-1){ref-type="fig"}

###### 

Click here for additional data file.

10.7717/peerj.7519/supp-3

###### Raw data for ADC patients in [Table 1](#table-1){ref-type="table"} and [Fig. 1](#fig-1){ref-type="fig"}

###### 

Click here for additional data file.

Additional Information and Declarations
=======================================

The authors declare there are no competing interests.

[Tao Yan](#author-1){ref-type="contrib"} conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.

[Kai Wang](#author-2){ref-type="contrib"} conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, authored or reviewed drafts of the paper, approved the final draft.

[Jichang Liu](#author-3){ref-type="contrib"} performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.

[Yukai Zeng](#author-4){ref-type="contrib"} analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, approved the final draft.

[Fenglong Bie](#author-5){ref-type="contrib"} contributed reagents/materials/analysis tools, approved the final draft.

[Guanghui Wang](#author-6){ref-type="contrib"} contributed reagents/materials/analysis tools, authored or reviewed drafts of the paper, approved the final draft.

[Jiajun Du](#author-7){ref-type="contrib"} conceived and designed the experiments, performed the experiments, approved the final draft.

The following information was supplied regarding data availability:

The raw measurements are available in [Table S1](#supp-1){ref-type="supplementary-material"}, [Table S2](#supp-2){ref-type="supplementary-material"}, and [Dataset S1](#supp-3){ref-type="supplementary-material"}.
