ewing 's sarcoma is a relatively rare malignant bone neoplasm that usually occurs in children and young adults and involves the major long bones , pelvis , and ribs .
however , primary pulmonary ewing 's sarcoma / primitive neuroectodermal tumor ( es / pnet ) is extremely rare . to the best of our knowledge ,
only eight cases of primary pulmonary es / pnet have been reported in the literature ( 1 - 4 ) .
a 67-yr - old man visited with a lung mass that had been detected incidentally on chest roentgenogram taken during the national insurance screening program .
the chest pa and left lateral films revealed an approximately 4-cm sized well - defined mass at the left lower lobe ( fig .
computed tomography showed a mass with a smooth margin and the tumor had well enhanced linear opacity inside of the contrast enhancement .
the mass was not connected to the pleurae , chest walls , or other adjacent organs ( fig .
the origin of the mass and metastasis was verified by examining the whole body bone scan , pet / ct scan with 2-[f ] fluoro-2-deoxy - d - glucose ( fdg ) , and brain magnetic resonance imaging ( mri ) . on bone scan , there were no active skeletal lesions .
the fdg - pet scan revealed intense and homogenous hypermetabolic activity with a metabolic defect at the left lower lobe of the lung .
except for the lung lesion , there was no abnormal hypermetabolic lesions or metabolic defects .
therefore we confirmed the lung was the primary focus of the mass , and there were no distant metastases .
a percutaneous needle biopsy was performed with 19 g thru cut needle under fluoroscopic guidance .
hematoxylin and eosin ( h - e ) staining showed a solidly packed round cell pattern with a striking uniformity .
the individual cells had a small round to ovoid nucleus with a distinctly unclear membrane , fine powdery chromatin , and one or two minute nucleoli .
some of the cells had irregularly vacuolated cytoplasm secondary to glycogen deposition , which was positive for periodic acid schiff ( pas ) stain ( fig .
the other markers including cytokeratin ( ck ) , small cell lung cancer ( sclc ) , chromogranin , ck7 , ck19 , and thyroid transcription factor 1 ( ttf-1 ) were all negative .
vimentin , synaptophysin , and p63 stained focally , and more than 90% of the cells were positive for ki-67 labeling .
all the pathological findings were compatible with a es / pnet of primary pulmonary origin .
after pathological diagnosis , surgical resection of the left lower lobe of the lung was done .
serial sections of the lung showed that the cut surface had a well demarcated round whitish soft mass , which had extensive tumoral necrosis .
it was 5 cm apart from the nearest bronchial resection margin and 0.5 cm from the nearest visceral pleura ( fig .
3 ) . using the tissue obtained after surgical resection , fluorescence in situ hybridization ( fish )
was performed using the lsi ewing sarcoma breakpoint region 1 ( ewsr1 ) 22q12 dual color break apart rearrangement probe and revealed ewsr1 22q12 rearrangement in 82% ( 164 out of 200 cells ) ( fig .
ultimately , the diagnosis was established to be a 4-cm sized es / pnet arising primarily from the lung with no regional invasion to the bronchi , visceral , or parietal pleurae .
in addition , there was no perihilar lymph node invasion ( all 4 of 4 ) or distant metastasis .
after surgery , the patient was administered with combination chemotherapy with vincristin , actinomycin , and cyclophosphamide .
since the first description of es and extraskeletal ewing 's sarcoma by james ewing and tefft et al . , these two conditions have been confused histologically with other small cell tumors , including pnet ( 5 , 6 ) , but recent immunoperoxidase and cytogenic studies indicated that pnet and es are the same entity showing varying degrees of neuroectodermal differentiation , and they were categorized into a group known as the ewing family of tumors ( 7 ) .
the es / pnet family is an uncommon malignant neoplasm , and shares common histological features of closely packed small primitive round cells .
it most often arises in the soft tissues and bones but has rarely been reported in other sites , such as the ovary , testis , uterus , kidney , pancreas , palate , myocardium , and lung ( 1 , 7 - 10 ) .
the morphological features of intrapulmonary tumors are similar to those of the es / pnet in a variety of other locations . in this case the patient was 67 yr old , which was an unusual age compared with previously reported es / pnet cases .
most of them were from child to young adults except one case ( 4 ) .
the diagnosis of a tumor is made using several modalities such as light microscopy , immunohistochemistry , and cytogeneteics ( 1 ) .
immunohistochemical and histochemical staining positive for glycogen ( pas , 80% ) , neuron - specific enolase ( 60% ) , s-100 protein ( 50% ) , and mic-2 marker ( 90% ) , as well as negative findings for leukocyte common antigen , epithelial membrane antigen , cytokeratin , desmin , vimentin , myoglobin , and glial fibrillary acidic protein are indicative of es / pnet ( 11 , 12 ) . among them , the p30/32 cell surface antigen ( also known as the mic2 gene product ) , which can be detected by antibodies such as hba71 and o13 , and the reciprocal translocation of the long arms of chromosomes 11 and 22 t ( 11;22)(q24;q12 ) , which results in the formation of chimeric transcripts of ews / fli-1 , are believed to be characteristic of this family of tumors ( 1 ) . in this case
the mic-2 immunoreactivity and rearrangement of ewsr1 were observed . because primary pulmonary es / pnet is very rare
, we tested several markers for small cell carcinomas such as ck , sclc , chromogranin , ck7 , ck19 , and ttf-1 , which were all negative . ultimately , fish revealed an ewsr1 22q12 rearrangement , which confirmed the diagnosis cytogenetically .
the most common ct finding of es / pnet reported is a heterogeneously enhancing mass .
occasionally , a central , non - enhancing , low - density area is seen within the mass ( 12 ) . in our case
, well - enhanced linear opacity was observed inside the mass . in the fdg - pet scan ,
the suv was 6.22 , which is comparable with that in a previous study of ewing sarcoma ( suv of 4.542.79 ) . in the diagnosis of es
/ pnet , a fdg pet scan is not diagnostic , but the sensitivity and specificity of the examination is quite high , 96% and 78% , respectively ( 13 ) .
the treatment of es / pnet is aggressive with the most effective treatment being a surgical resection with combination chemotherapy and high - dose radiation therapy . when resectable , the surgical excision must be wide in accordance with classic oncological principles ( 14 , 15 ) .
a lobectomy including the mass lesion was performed and combination chemotherapy was subsequently administered . in conclusion , we experienced a primary pulmonary es / pnet . although the primary pulmonary es / pnet is an extremely rare soft tissue sarcoma , it should be considered in the differential diagnosis of a primary pulmonary mass .
 extraskeletal ewing 's sarcoma ( ees ) is a branch of neuroectodermal tumor ( pnet ) , which is very rare soft tissue sarcoma . 
 we report a case of ees / pnet arising is the lung of a 67-yr - old man . 
 computed tomography , bone scintigraphy , and positron emission tomography confirmed the mass to have a primary pulmonary origin . 
 the mass showed positive reactivity in the periodic acid schiff ( pas ) stain and mic-2 immunoreactivity in immunohistochemical stain . 
 fluorescence in situ hybridization ( fish ) was performed , which revealed an ewsr1 ( ewing sarcoma breakpoint region 1 ) 22q12 rearrangement . 
 the diagnosis was confirmed both pathologically and genetically . 
 the mass lesion was resected , and the patient is currently undergoing chemotherapy . 
INTRODUCTION
CASE REPORT
DISCUSSION