Diagnostic problems and immune contexture in a case of cecal medullary carcinoma

Abstract

Medullary carcinoma (MC) of the colon has recently been described as a separate variant of colorectal carcinoma, associated with microsatellite instability. Despite its morphological similarities to poorly differentiated adenocarcinomas (PDAs) and neuroendocrine carcinomas (NECs), the prognosis seems to be more favorable. A case of an adult female patient who presented with obstructive ileus due to a right-sided colon mass is reported. A specimen of right hemicolectomy was received and a large tumor was observed at the cecum. Tumor sections revealed a poorly differentiated carcinoma, without elements of intestinal differentiation on histologic or immunohistochemical examination. Further investigation lead to the diagnosis of MC of the cecum. The majority of lymphocytic populations of the microenvironment were granzyme B and T-cell intracellular antigen-1 (TIA-1) positive, with an abundant intraepithelial compartment. There were only a few Forkhead box P3(FOXP3) positive T-regulatory cells. It is emphasized that an undifferentiated large bowel carcinoma characterized by black-tan color on gross examination, expressing epithelial keratins and calretinin, proven to be microsatellite unstable with abundant intratumoral cytotoxic lymphocytes should be diagnosed as MC.