1 . analysis of tumor cases over eight years among the samples for which the department of veterinary pathology , gifu university , 
 received requests for histological examination from other institutions during the eight - year 
 period from 2005 to 2012 , we used data only from the institutions located in gifu prefecture 
 to understand the status of tumor development in dogs by breed in the prefecture . 11 .
distribution of age at the time of diagnosis of tumor cases classified by sex of the requested samples , only tumor cases were extracted for the analysis of age 
 distribution of tumor cases classified by sex .
statistical analysis was conducted using 
 jmp11 analysis software ( sas institute inc . , tokyo , japan ) , and the mean age by sex and 
 standard deviation were calculated ; the wilcoxon rank sum test was conducted at a 
 significance level of less than 5% .
. ratios between benign and malignant tumors by dog breed we calculated the ratios between benign and malignant tumors in dogs by breed for the tumor 
 cases included in this study .
the comparison of the ratios of benign and malignant tumors by breed was statistically 
 calculated using the chi - square test with a significance level of less than 5% using r 
 ( version 3.2.2 ) . additionally , we performed residual analysis to clarify and confirm this 
 further .
classification of tumors in dogs by breed tumors were classified as shown in table 
 1table 1.tumor classification by breed and incidencetumor sitesno .
of casesincidence of tumor sites ( % ) bgbmdcgckcwdaxfbgrlrmarmixotherpappdpgpomschsibssdszyt1skin and adnexa1,23330.929.533.328.117.630.018.430.441.235.531.534.433.522.830.258.312.135.428.927.526.015.22gastrointestinal system , including oral cavity73318.420.110.011.48.818.617.434.815.519.714.121.516.76.320.617.924.230.820.118.123.115.23mammary glands71618.013.70.017.841.224.341.54.36.412.833.714.415.238.028.67.136.412.310.87.014.933.94not available and other tissue1,30332.736.756.742.732.427.122.630.436.931.920.729.734.632.920.616.727.321.540.247.435.935.7total3,985100100100100100100100100100100100100100100100100100100100100100100tumor incidence by dog breed and tumor site was statistically calculated by the 
 chi - square test .
these 
 results indicate that between each dog species and whole dog species has a significant 
 difference in table 1 
 ( p<0.05 ) .
additionally , we performed residual analysis to clarify 
 and confirm this further . a significantly high incidence ( p<0.05 ) 

is indicated by values in bold , and a significantly low incidence 
 ( p<0.05 ) is indicated by values in bold and underlined font . 

tumors in the skin and adnexa accounted for 30.9% of all tumors , those in the 
 gastrointestinal system adnexa accounted for 18.4% , and mammary gland tumors accounted 
 for 18.0% ; the tumors in these four sites accounted for approximately 70% of all 
 tumors .
the incidence of mammary gland tumors was found to be higher in small dogs , 
 such as ck , dax , mar , pap , pd , pom and yt , and lower in large dogs . in reference to the report by brnden et al . .
to analyze the common sites for the development of 
 tumors in dogs by breed , we determined the total number of tumor cases by calculating 
 multiple tumors individually , i.e. , when multiple , different types of tumors developed in 
 the same dog , each tumor was separately included in the calculation .
however , with regard to 
 breast tumors , since the formation of numerous tumors is common and each tumor is given a 
 different definitive diagnosis , it was difficult to classify each of the tumors separately . 
 therefore , in such cases , only the most malignant tumor among the tissues submitted for 
 pathological examination was selected for calculation .
tumor incidence by dog breed and tumor site was statistically calculated by the 
 chi - square test .
these 
 results indicate that between each dog species and whole dog species has a significant 
 difference in table 1 
 ( p<0.05 ) . additionally , we performed residual analysis to clarify 
 and confirm this further .
a significantly high incidence ( p<0.05 ) 
 is indicated by values in bold , and a significantly low incidence 
 ( p<0.05 ) is indicated by values in bold and underlined font . 

tumors in the skin and adnexa accounted for 30.9% of all tumors , those in the 
 gastrointestinal system adnexa accounted for 18.4% , and mammary gland tumors accounted 
 for 18.0% ; the tumors in these four sites accounted for approximately 70% of all 
 tumors .
the incidence of mammary gland tumors was found to be higher in small dogs , 
 such as ck , dax , mar , pap , pd , pom and yt , and lower in large dogs .
the incidence of tumor sites by dog breed was statistically calculated using the chi - square 
 test with a significance level of less than 5% using r ( version 3.2.2 . ) . additionally , we 
 performed residual analysis to clarify and confirm this further .
analysis of the number of domestic dogs by breed and crude incidence of tumors in dogs 
 in gifu prefecture 21 .
the number of domestic dogs based on the dogs receiving antirabic vaccination in 2011 
 in gifu prefecture a request for a questionnaire survey regarding the number of domestic dogs by breed was 
 sent to 42 municipalities through postal mail or email .
for the types of dog breed , 20 
 breeds , including crossbreeds , were selected ( table 
 2table 2.abbreviated terms for the dog breeds included in this study and the number of 
 tumor casesdog breedabbreviated wordno . of tumor casesdachshunddax407golden retrievergr388labrador retrieverlr304shih tzusz281sibasib204welsh corgicg185shetland sheepdogssd171beaglebg139yorkshire
terrieryt112maltese dogmar92pugpg84papillonpap79chihuahuacw70schnauzersch65poodlepd63cavalier king charles spanielck34pomeranianpom33bernese mountain dogbmd30french bulldogfb23mixed breedmix713other breedother508total 3,985a ) dachshund , schnauzer and poodle : in the original data , these dogs were not 
 classified into miniature or standard .
therefore , all of these dogs were calculated as 
 the same type . ) in reference to shimamura s report . for the number of domestic dogs by breed ,
the number of dogs that received 
 antirabic vaccination ( rv ) was selected , since these data were considered to reflect the 
 current status most appropriately , and the number of domestic dogs for the 20 breeds was 
 investigated for the period from april 2011 to march 2012 .
although the official data for 
 the number of dogs receiving rv are published by each of the prefectural and municipal 
 veterinarian associations as well as the ministry of health , labour and welfare ( mhlw ) , the 
 figure represents the total number of dogs receiving rv , and the breakdown by dog breed is 
 unknown .
a ) dachshund , schnauzer and poodle : in the original data , these dogs were not 
 classified into miniature or standard . therefore , all of these dogs were calculated as 
 the same type .
22 . the crude yearly incidence of tumors in dogs and the crude yearly incidence of 
 malignant tumors in dogs based on the number of dogs receiving antirabic vaccination in 2011 
 in gifu prefecture to identify the number of tumor cases in dogs , the tumor cases from veterinary hospitals 
 and clinics located only in gifu prefecture were extracted to calculate the samples for 
 which the department of veterinary pathology of the gifu university received a request for 
 histological examination in 2011 , as stated in the previous section .
with regard to the dog 
 breeds , 20 breeds were selected , including crossbreeds .
the crude incidences of tumors and malignant tumors were calculated in the following 
 manner , using the number of dogs receiving rv in 2011 in gifu prefecture and the data 
 mentioned above .
crude incidence of tumors ( % ) = the number of tumor cases ( the above - mentioned data )  the 
 number of domestic dogs ( number of dogs receiving rv in 2011 )  100 crude incidence of malignant tumors ( % ) = the number of cases of malignant tumor ( the 
 above - mentioned data )  the number of domestic dogs ( number of dogs receiving rv in 2011 )  
 100 the crude incidence of tumors and malignant tumors by dog breed was statistically 
 calculated by the chi - square test with a significance level of less than 5% using r
1 . analysis of tumor cases over eight years as of april 2012 ( mid - term ) , there were 131 veterinary hospitals and clinics in practice in 
 gifu prefecture . among them , approximately 23% or 31 hospitals and clinics requested the 
 department of veterinary pathology of the gifu university to conduct tests for tumors in 
 3,597 cases ( 1,598 male dogs ; 2,160 female dogs ; and 161 dogs of unknown sex ) over the 
 eight - year period from 2005 to 2012 . among the total of 3,597 tumor cases that presented for 
 pathological examination requests ,
388 cases were found to have more than one tumor , 
 excluding breast tumors , including 277 cases ( 6.95% ) with 2 different types of tumors and 41 
 cases ( 1.03% ) with 35 different types of tumors . including these multiple tumors , a total 
 of 3,985 tumors
distribution of the age at the time of diagnosis of tumor cases classified by sex in the analysis of age in all the samples , the mean age at which a tumor developed was 10.4 
  3.0 years ( mean  s.d . ) in male dogs and 10.4  2.8 years ( mean  s.d . ) in female dogs , 
 showing no significant difference between males and females ( fig .
2.distribution of the age at the time of diagnosis of tumor cases classified by sex . 

the age of the dogs diagnosed as tumor cases at the time of the examination request is 
 shown in the graph classified by sex .
analysis of age of the samples by pathological 
 classification revealed that the mean age of developing tumors in male dogs was 10.4  
 3.0 years ( mean  s.d . ) and that in female dogs was 10.4  2.8 ( mean  s.d . ) , showing 
 no significant difference in the age between males and females . ) .
distribution of the age at the time of diagnosis of tumor cases classified by sex . 

the age of the dogs diagnosed as tumor cases at the time of the examination request is 
 shown in the graph classified by sex .
analysis of age of the samples by pathological 
 classification revealed that the mean age of developing tumors in male dogs was 10.4  
 3.0 years ( mean  s.d . ) and that in female dogs was 10.4  2.8 ( mean  s.d . ) , showing 
 no significant difference in the age between males and females .
. ratios between benign and malignant tumors by dog breed the proportion of malignant tumors in all dogs was revealed to be 57.5% .
the ratio of 
 malignant tumors was significantly lower ( p<0.05 ) in the following five 
 dog breeds : yorkshire terrier ( yt ) ( 32.1% ) , maltese dog ( mar ) ( 42.4% ) , poodle ( pd ) ( 44.4% ) , 
 shih tzu ( sz ) ( 48.0% ) and dachshund ( dax ) ( 48.2% ) , while the proportion of malignant tumors 
 was significantly higher in the following seven dog breeds : labrador retriever ( lr ) ( 63.2% ) , 
 welsh corgi ( cg ) ( 65.9% ) , shiba ( sib ) ( 68.1% ) , shetland sheepdog ( ssd ) ( 69.0% ) , chihuahua 
 ( cw ) ( 70.0% ) , beagle ( bg ) ( 73.4% ) and bernese mountain dog ( bmd ) ( 80.0% ) 
 ( p<0.05 ) ( fig . 3fig .
the ratio of tumor and malignant 
 tumors by dog breed was statistically calculated by the chi - square test .
the result 
 was  chi - squared=130.65 , p - value < 2.2e-16  .
these results indicate 
 that between each dog species and whole dog species has a significant difference in 
 fig . 3 ( p<0.05 ) . 

the 
 bold black line shows the mean of the ratio of malignant tumors in all dogs .
 : the 
 ratio of malignant tumors was significantly lower in the following five dog breeds : yt 
 ( 32.1% ) , mar ( 42.4% ) , pd ( 44.4% ) , sz ( 48.0% ) and dax ( 48.2% ) 
 ( p<0.05 ) , while the ratio of malignant tumors was significantly 
 higher in the following seven dog breeds : lr ( 63.2% ) , cg ( 65.9% ) , sib ( 68.1% ) , ssd 
 ( 69.0% ) , cw ( 70.0% ) , bg ( 73.4% ) and bmd ( 80.0% ) ( p<0.05 ) . ) .
the ratio of tumor and malignant 
 tumors by dog breed was statistically calculated by the chi - square test .
the result 
 was  chi - squared=130.65 , p - value < 2.2e-16  .
these results indicate 
 that between each dog species and whole dog species has a significant difference in 
 fig . 3 ( p<0.05 ) . 
 additionally , we performed residual analysis to clarify and confirm this further .
the 
 bold black line shows the mean of the ratio of malignant tumors in all dogs .  : the 
 ratio of malignant tumors was significantly lower in the following five dog breeds : yt 
 ( 32.1% ) , mar ( 42.4% ) , pd ( 44.4% ) , sz ( 48.0% ) and dax ( 48.2% ) 
 ( p<0.05 ) , while the ratio of malignant tumors was significantly 
 higher in the following seven dog breeds : lr ( 63.2% ) , cg ( 65.9% ) , sib ( 68.1% ) , ssd 
 ( 69.0% ) , cw ( 70.0% ) , bg ( 73.4% ) and bmd ( 80.0% ) ( p<0.05 ) .
analysis of the ratios between the benign and malignant tumors by dog breed showed that 
 smaller dogs tended to have a higher proportion of benign tumors .
classification of tumors by dog breed in the analysis of the 3,985 tumors in terms of the location of tumor development , tumors 
 were found most often in the skin and surrounding tissues , with 1,233 cases accounting for 
 30.9% . in particular , the pug ( pg ) and golden retriever ( gr ) breeds had the highest 
 incidence of tumors in the skin and surrounding tissues with an incidence of 58.3% and 
 41.2% , respectively , while yt and pomeranian ( pom ) had a lower incidence of 15.2% and 12.1% , 
 respectively .
gastrointestinal tumors were the second most common tumors and were found in 
 733 cases accounting for 18.4% .
gastrointestinal tumors included the areas from the oral 
 cavity to the anus , and intraoral melanoma was particularly common , accounting for 55% of 
 all gastrointestinal tumors as an intraoral tumor , followed by perianal tumors that 
 accounted for 21% .
breast tumors were the third most common tumors and were found in 716 
 cases that accounted for 18.0% .
smaller dog breeds had greater proportion of breast tumors , 
 which accounted for 41.5% in dax , 41.2% in cavalier king charles spaniel ( ck ) , 38.0% in 
 papillon ( pap ) , 36.4% in pom , 33.9% in yt and 33.7% in mar , while medium to large dog breeds 
 had fewer breast tumors , which accounted for 0% in bmd , 7.1% in pug ( pg ) , 6.4% in gr , 7.0% 
 in ssd , 10.8% in sib and 12.8% in lr .
with regard to mast cell tumors , they were found more 
 often in the two breeds , pg and bmd , accounting for 46.4% and 23.3% , respectively .
analysis of the number of domestic dogs by breed and crude incidence of tumors in dogs 
 in gifu prefecture 21 . the number of domestic dogs in gifu prefecture by breed based on the number of dogs 
 receiving rv in 2011 we conducted a questionnaire survey in 42 municipalities in gifu prefecture , and 29 of the 
 42 ( approximately 69% ) responded . with regard to the number of domestic dogs , the number of 
 dogs receiving rv during the period from april 2011 to march 2012 was 93,234 according to 
 the gifu veterinary medical association , and information
about 76,316 dogs or approximately 
 82% of the total number of rv dogs was collected through the questionnaire survey .
the 
 numbers of domestic dogs in gifu prefecture revealed by this questionnaire survey included 
 18,357 mixed breeds ( mix ) ( 24.1% ) , 9,609 dax ( 12.6% ) , 8,609 sib ( 11.3% ) , 5,017 pd ( 6.6% ) and 
 4,873 cw ( 6.4% ) ; this demonstrated the high popularity of small dog breeds except for mix 
 and sib , while large dog breeds were fewer , namely , 2,312 lr ( 3.0% ) and 1,213 gr ( 1.6% ) .
the 
 top 5 dog breeds including mix accounted for 60% of all the dogs ( table 3table 3.crude tumor incidence and crude malignant tumor incidence by dog breeddog breedregistration volumebreeding ratiosample volumecrude incidence ratemalignant sample volumemalignant crude incidence rate ( % ) dax9,60912.6710.7*430.4sib8,60911.3410.5*280.3*pd5,0176.680.2*10.0*cw4,8736.4130.3*90.2*lr2,3123.0612.6*431.9*sz2,0212.6301.5*150.7cg1,9272.5573.0*402.1*pap1,8092.4241.3*130.7bg1,6362.1382.3*301.8*yt1,5542.0231.5*60.4pom1,4321.910.1*10.1*gr1,2131.6524.3*342.8*sch1,0611.4161.5*80.8ssd8771.1222.5*151.7*mar8311.1172.0*50.6ck7541.091.260.8pg6520.9142.1*60.9fb5340.740.740.7bmd1400.2117.9*96.4*mix18,35724.11160.6*660.4*other11,09814.5860.8*470.4*total 76,316100.07140.94290.6by calculating the number of domestic dogs and the ratio of each dog breed , crude 
 tumor incidence and crude malignant tumor incidence were analyzed based on the number 
 of samples for each dog breed obtained over a one - year period of time .
tumor crude 
 incidence by dog breed was statistically calculated by the chi - square test .
the result 
 was " chi - squared=476.01 , p - value < 2.2e-16 " .
these results indicate 
 that between each dog species and whole dog species has a significant difference in 
 table 3 ( p<0.05 ) . 
 additionally , we performed residual analysis to clarify and confirm this further . 

significantly high incidences are indicated by p<0.05  * , and 
 significantly low incidences are indicated by p<0.05 *. the crude 
 tumor incidence was found to be low in dax , sib , pd , cw , pom , mix and other breeds 
 ( p<0.05 ) , while it was high in lr , sz , cg , pap , bg , yt , gr , sch , 
 ssd , mar , pg and bmd ( p<0.05 ) . the crude incidence of malignant 
 tumors was also calculated in the same manner ; it was found to be low in sib , pd , cw , 
 pom , mix and other breeds ( p<0.05 ) , but high in lr , cg , bg , gr , 
 ssd and bmd ( p<0.05 ) . ) . by calculating the number of domestic dogs and
the ratio of each dog breed , crude 
 tumor incidence and crude malignant tumor incidence were analyzed based on the number 
 of samples for each dog breed obtained over a one - year period of time .
tumor crude 
 incidence by dog breed was statistically calculated by the chi - square test .
the result 
 was " chi - squared=476.01 , p - value < 2.2e-16 " .
these results indicate 
 that between each dog species and whole dog species has a significant difference in 
 table 3 ( p<0.05 ) . 
 additionally , we performed residual analysis to clarify and confirm this further . 

significantly high incidences are indicated by p<0.05  * , and 
 significantly low incidences are indicated by p<0.05 *. the crude 
 tumor incidence was found to be low in dax , sib , pd , cw , pom , mix and other breeds 
 ( p<0.05 ) , while it was high in lr , sz , cg , pap , bg , yt , gr , sch , 
 ssd , mar , pg and bmd ( p<0.05 ) . the crude incidence of malignant 
 tumors was also calculated in the same manner ; it was found to be low in sib , pd , cw , 
 pom , mix and other breeds ( p<0.05 ) , but high in lr , cg , bg , gr , 
 ssd and bmd ( p<0.05 ) .
the crude incidence of tumors in dogs and the crude incidence of malignant tumors in 
 dogs in 2011 in gifu prefecture with regard to the number of samples for which examination was requested from the 
 university during the one - year period ( 2011 ) , most requests were for mix , with 116 samples , 
 followed by dax with 71 , lr with 61 , cg with 57 , gr with 52 and sib with 41 samples ( table 3 ) .
using the samples collected for 
 pathological examination , the crude incidences of tumors by dog breed were calculated for 
 reference .
our results showed that the crude incidence of tumors was significantly low in 
 pom at 0.1% , pd at 0.2% , cw at 0.3% , sib at 0.5% , dax at 0.7% , and mix at 0.6% 
 ( p<0.05 ) , while it was significantly high in pap at 1.3% , sz at 1.5% , 
 yt at 1.5% , sch at 1.5% , mar at 2.0% , pg at 2.1% , bg at 2.3% , ssd at 2.5% , l r at 2.6% , cg 
 at 3.0% , gr at 4.3% , and bmd at 7.9% ( p<0.05 ) .
in addition , the crude 
 incidence of malignant tumors was calculated in the same manner , and it was significantly 
 low in sib at 0.3% , pd at 0.0% , cw at 0.2% , pom at 0.1% , and mix at 0.4% 
 ( p<0.05 ) , and it was significantly high in lr at 1.9% , cg at 2.1% , bg at 
 1.8% , gr at 2.8% , ssd at 1.7% , and bmd at 6.4% ( p<0.05 ) .
the analysis of tumor development in dogs by breed in gifu prefecture revealed the 
 following characteristics : common breeds of dogs , such as mix and dax , showed a 
 high number of tumor cases , and uncommon breeds of dogs , such as gr and lr , also showed a 
 high number of tumor cases ; in contrast , common breeds of dogs , such as sib , showed a low 
 number of tumor cases , suggesting the possibility that the crude tumor incidence in dogs 
 varied depending on the dog breed .
the analysis of the ratio between benign and malignant 
 tumors by dog breed showed that small dog breeds tended to have a greater proportion of 
 benign tumors .
although the ratio of malignant tumors in this study was 57.5% , there was a 
 swiss report in which malignant tumors accounted for 47.07% of all investigated tumors in 
 the survey .
this difference was considered to be 
 caused by the differences in the types of dog breeds and breeding environment ; however , 
 further investigation is necessary to clarify this point . with regard to the samples 
 submitted for pathological examination
, there is a possibility of potential bias with regard 
 to the collection of the samples , since the primary veterinary hospital or clinic may have 
 sent fewer samples of benign tumors or more samples , of malignant tumors , keeping in mind 
 that the  university 
with regard to analysis of the most commonly developed organ systems , tumors were found 
 most frequently in the skin and surrounding tissues , similar to reports from other countries 
 [ 7 , 10 , 14 ] , but the organ systems showing a high frequency of 
 tumors after the skin and surrounding tissues , differed slightly from reports from other 
 countries .
this is considered to be due to the differences in the types and incidence of dog 
 breeds , e.g. , reports from other countries included higher number of large dog breeds .
with regard to breast tumors , dogs were divided into the high incidence group , including 
 ck , dax , mar , pap , pd , pom and yt , and the low incidence group , including bmd , gr , lr , mix , 
 pg and ssd .
itoh et al . have also reported that small dog breeds have a 
 lower risk of malignant breast tumors compared to another types of dogs . in some of the reports from other countries 
 concerning breast tumors in dogs , dogs , such as boxer , cocker spaniel , english springer 
 spaniel , dax , pointer , pd and boston terrier , had a higher incidence of breast tumors [ 14 , 16 ] ; further , 
 contrary to the results of our study , there was a report that breast tumors developed more 
 frequently in large dog breeds , such as leonberger , irish wolfhound and bmd .
it has been known for some time now that mast cell 
 tumors develop more frequently in the mastiff - type boxer dog breeds .
mast cell tumors have been found with a high frequency in pg , bmd and 
 fb , which are related to mastiff - type breeds in the same manner as boxer breeds [ 21 , 23 ] , and 
 breeds with a lower frequency for such tumors were also revealed to be ck , pom , ssd and 
 yt .
frequently , data registered at municipalities do not reflect the deaths of domestic dogs 
 accurately .
therefore , there is a possibility that many dogs as old as 25 years and even 
 older exist in the database , and the research of hayashidani , et al
.   also showed that there is a possibility that the data 
 of elderly dogs that are not alive have not been removed from the records . in this study , 
 there were not many domestic dogs older than 20 years ; therefore , the reliability of the 
 municipal data collected in this study was considered to be high . with regard to the fewer 
 domestic dogs younger than 3 years noted in the age distribution , it was probably caused by 
 unregistered younger dogs ( rv
the 
 performance rate of rv in gifu prefecture has been 79.580.9% every year ( 2008 to 2011 ) , 
 which was higher than the national mean of 72.8% ( 2011 ) .
this shows the regional 
 characteristics of gifu prefecture , and it was considered that the basic data were thus 
 reliable .
the decreasing number of domestic dogs leads to a bias in the age distribution . 
 when more elderly dogs are present than younger dogs , the tumor incidence should be 
 calculated after adjustment for age to be accurate , because higher figures would be noted 
 otherwise .
however , at present , it is difficult to obtain information regarding age for each 
 breed from the municipal data , and we therefore decided to investigate the crude tumor 
 incidence .
the crude incidence of 0.9% seems to be slightly lower than the tumor incidence reported 
 overseas , ranging from 0.96% to 4.82% [ 14 , 17 , 20 ] , which may 
 be the influence of basic data .
it was considered that the tumor incidence calculated in 
 this study may be lower than the actual incidence , because the performance rate of rv was 
 not 100% of the population , and there is a possibility that the primary institutions may 
 only have sent approximately 24% of the tumor samples for examination .
in addition , since 
 the number of dogs with tumors that visit a veterinary hospital ( some dogs may not visit a 
 hospital ) , the percentage of dogs diagnosed with a tumor at veterinary hospitals or clinics 
 ( some dog owners do not want to have examinations ) and the percentage of cases for which a 
 sample is sent to the university for pathological examination ( some samples may be sent to 
 another pathology laboratory ) influenced the tumor incidence , it was considered that there 
 is a possibility that the calculation of the crude tumor incidence and crude malignant tumor 
 incidence in this study may have underestimated the reality . to control such bias ,
measures 
 should be adopted to select target animals randomly in future studies . although the crude tumor incidence calculated by breed may be lower than it should be due 
 to the problems with the size of the population and the number of samples collected ,
it is 
 considered that the incidence by breed and by organ would not be easily affected by the 
 changes in the number of samples or age distribution .
most domestic dogs in japan are of small breeds , such as those kept mainly inside the 
 house ; in our study , only three large dog breeds ( lr , gr and bmd ) were present among all the 
 20 selected breeds , which differed largely from the reports from other countries [ 6 , 9 , 20 ] .
since the crude tumor incidence was affected by the 
 type of breed and the body size , it is considered that the data obtained in this study are 
 unique to japan , where most domestic dogs are small- and medium - sized , differing from data 
 from other countries .
it is necessary to investigate the relationship between the breeding 
 environment and the crude tumor incidence in future studies .
we consider that , in addition to improving the accuracy of the survey data , it is necessary 
 to promote antirabic vaccination , to utilize the municipal database , and to obtain an 
 accurate number of bred animals by adding an item in the surveys , such as a census , to 
 investigate the status of bred animals . in addition , it is important to use domestic 
 japanese data to manage cancers in dogs in japan , instead of using data obtained from other 
 countries , where the size of the dogs is mostly large , considering the differences in dog 
 size in japan and other countries .
 we analyzed the status of tumor development in dogs by breed based on tumor cases that 
 presented to the department of veterinary pathology of the gifu university for diagnostic 
 examinations over eight years ( 20052012 ) . 
 we also calculated the crude incidence of 
 tumors in dogs by breed based on the results of a survey conducted in 2011 in gifu 
 prefecture . 
 the most common sites of tumor development included the skin , digestive organs 
 and mammary glands . 
 smaller dogs showed a tendency to have a higher incidence of breast 
 tumors . 
 we thus identified dog breeds with a higher crude incidence of tumors ( bernese 
 mountain dog , golden retriever , corgi , etc . ) and those with a lower crude incidence of 
 tumors ( pomeranian , poodle , chihuahua , etc . ) . unlike the current trends for domestic dogs 
 in the us and 
 europe , japan has a higher number of small dogs as pets ; it is therefore 
 necessary to develop a policy for canine cancer specific to japan . 
MATERIALS AND METHODS
RESULTS
DISCUSSION