the incidence of synchronous lesion in patients with colorectal carcinoma is up to 5% [ 1 , 2 ] . we describe a rare case of synchronous neuroendocrine tumor ( net ) and adenocarcinoma present at two different locations but in the same segment of the colon . an 83-year - old male presented with two episodes of bleeding per rectum during hospitalization for coronary artery stenting . his colonoscopic examination revealed two ulceroproliferative tumors , one in the sigmoid colon and another in the descending colon , approximately 20 and 40 cm , respectively , from the anal verge . a contrast - enhanced ct scan of the abdomen confirmed the presence of these two tumors . a clinical diagnosis of synchronous carcinoma colon was made and the patient was subjected to left hemicolectomy . at laparotomy , both the tumors were found confined to the colonic wall without any evidence of lymph node enlargement or dissemination . the sct was larger in size involving 2/3 colonic circumference , whereas the dct was smaller and involved nearly half of the colonic circumference ( fig .  1 ) the proximal tumor in the descending colon turned out to be neuroendocrine cancer and the distal one in the sigmoid colon was adenocarcinoma . the proximal tumor in the descending colon turned out to be neuroendocrine cancer and the distal one in the sigmoid colon was adenocarcinoma . 2a  d ) revealed a cellular neoplasm composed of round to polygonal tumor cells with pleomorphic nuclei , fine granular chromatin and prominent nucleoli arranged in diffuse sheets , insular pattern and variable organoid pattern . dct , the smaller of the two , was diffusely positive for synaptophysin and neuron - specific enolase ( nse ) . however , cd56 and chromogranin - a were negative in the same tumor cells . on the other hand , sct that had typical morphology of adenocarcinoma was completely negative for cd56 , synaptophysin , chromogranin a and nse . therefore , based on histomorphology and immunohistochemistry , the sct was diagnosed as well - differentiated adenocarcinoma and the dct was diagnosed as neuroendocrine carcinoma grade 3 . both the tumors had invaded the subserosa without any lymph nodal involvement . 
 figure  2:microscopic appearance of the neuroendococrine carcinoma . ( a ) ( h&e 20 ) showing round to polygonal tumor cells with pleomorphic nuclei , fine granular chromatin and prominent nucleoli arranged in diffuse sheets , insular pattern and variable organoid pattern . immunohistochemistry showed that the tumor was ( b ) diffusely positive for synaptophysin and ( c ) nse . ( a ) ( h&e 20 ) showing round to polygonal tumor cells with pleomorphic nuclei , fine granular chromatin and prominent nucleoli arranged in diffuse sheets , insular pattern and variable organoid pattern . immunohistochemistry showed that the tumor was ( b ) diffusely positive for synaptophysin and ( c ) nse . . approximately 27% of the gastrointestinal ( gi ) tract , nets are located in the descending colon and rectum . second primary malignancy ( spm ) , synchronous or metachronous , in the gi tract , lung or prostate has been reported in 1355% of patients with an net [ 5 , 6 ] . conversely , on immunohistochemical staining , neuroendocrine cells can be detected in up to 41% of colorectal adenocarcinoma . few authors suggest common link between the pathogenesis of the colorectal net and adenocarcinoma [ 8 , 9 ] . kato et al .   reported a ck20 positive ( a common marker found in colorectal adenocarcinoma ) large cell net that occurred synchronously to a colorectal adenocarcinoma , suggesting the theory that different types of gi neoplasm might originate from a common stem cell clone which might share a similar genetic mutation(s ) during early oncogenesis . if the net is completely resected , the 5-year survival rate has been reported to be 61% . however , metastatic and non - resectable disease is treated with radiation therapy in combination with systematic chemotherapy . adenocarcinoma and net occurring separately in the same segment of colon , as in the present case , are distinctly rare and have not been reported earlier . reported here , the preoperative diagnosis , based on colonoscopic appearance , was also adenocarcinoma . the differentiation that came as postoperative histological surprise is important since the net has a worse prognosis in comparison with adenocarcinoma . in conclusion , we report an net of the colon that coexisted with an adenocarcinoma , suggesting a possible common link between the pathogenesis of these two distinct entities . in addition , as the incidence of synchronous net and other primary malignancy is increasing , we recommend further screening for other primary malignancy in patients diagnosed with net for the prevention of late - stage diagnosis of synchronous malignancies .