Medullary Carcinoma of the Colon: Not as Favourable as Previously Thought?

Medullary carcinoma of the colon (MCC) is a rare, evolving subtype of colorectal cancer that is histologically and clinically distinct from poorly differentiated and undifferentiated adenocarcinoma. Comprehensive meta-analyses show that MCCs predominantly have a mismatch repair-deficient (MMRd) phenotype, which typically predicts a more favourable prognosis. We present a unique case involving a male patient with an aggressive presentation of colon cancer. Histopathology supported a diagnosis of MCC, initially staged as T3N0M0. Shortly after resection, the patient presented with rapidly progressing metastatic disease involving brain and subcutaneous metastases and subsequent mortality. MCC is an understudied subpopulation of colon cancers. Historically, the presence of MMRd in early-stage colon cancer predicts a favourable prognosis and also a lack of benefit from adjuvant chemotherapy. Whether this also extrapolates to MCCs remains unclear, and as such, the case presented highlights the uncertainty in the current evidence base. Further research is warranted to help inform robust clinical management.