Zeitschrift für Krebswissenschaft und -forschung
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Medullary Carcinoma of Colon: Pathologists Dilemma

Kasturi Saikia, Ejas Palathingal Bava, Qing Chang*

Medullary carcinoma of the colon is a rare tumor that has a unique and sometimes varied histologic profile, including a solid architecture with poor glandular differentiation, undifferentiated cellular morphology, an aberrant immunophenotype, and DNA microsatellite instability. Patients with medullary carcinoma have a better prognosis than those with other colon malignancies, but this rare tumor is often misdiagnosed. Here we report the case of a 77- year-old woman who presented with gastrointestinal bleeding and a 1-year history of anemia. A right-sided cecal mass was shown to harbor a tumor that had not spread to the lymph nodes. Interestingly, her tumor was positive for expression of Caudal-type homeobox transcription factor 2 (CDX2) and negative for the Keratin 20, which is unusual for this entity. However, overall cellular morphology and DNA microsatellite instability indicated by loss of expression of the mismatch repair proteins MLH1 and PMS2 supported a diagnosis of medullary carcinoma rather than a conventional adenocarcinoma of the colon. A refined understanding of the histologic and genetic as well as clinical phenotypes of medullary carcinoma of the colon is needed to prevent its misdiagnosis as other more aggressive colonic adenocarcinomas.