To investigate the clinical and immunohistochemical features, treatment and prognosis of medullary carcinoma of colon (MC) .

The clinical data of 9 patients with colonic MC from March 2019 to March 2022 were collected retrospectively, the clinicopathologic and molecular pathological features were analyzed with literature review.

Of the 9 patients, five were male and 4 were female, aged 30~84 years, 89% of them were in the right colon, seven cases were in Stage Ⅰ~Ⅱ, two cases were in Stage Ⅲ. The histopathologic features of the tumor were patchy and streaked infiltration of atypical cells, unclear cell boundaries, eosinophilic cytoplasm, vacuolated nuclei and prominent nucleoli, multiple lymphocyte infiltrates into the stroma and some of the tumor cells. The results of immunohistochemistry showed that MLH1 and PMS2 were absent in 8 cases, while CD20, CDX2 and P53 were mostly negative, which were different from common adenocarcinoma. No recurrence was found in the postoperative follow-up.

Medullary carcinoma of the colon is a rare poorly differentiated or undifferentiated tumor of the colon. Its clinical manifestation and immunohistochemical features are obviously different from those of common adenocarcinoma, but the prognosis is relatively good.