S2043 Hiding Mantle Cell Lymphoma

Abstract

Discussion: The differential diagnosis for poorly-differentiated colonic tumors includes poorly-differentiated adenocarcinoma (PDA), neuroendocrine tumor (NET), MCC, and metastasis. This ambiguity has led to tumor misidentification in up to 66% of MCC cases; however, several key features can distinguish among these carcinomas. MCC displays negative chromogranin and synaptophysin staining, unlike NET. MCC almost invariably has high MSI and is infrequently CK20 and CDX-2 positive, unlike PDA. Clinically, MCC is more likely to present in the eighth decade, in females, and in the right colon than NET or PDA. MCC frequently follows an indolent course with good prognosis, while PDA often grows and spreads aggressively. While this case had a uniquely young age of presentation, it otherwise exhibits known clinical and histological features of MCC. As familiarity with these features rises and the use of MSI testing expands, accurate diagnosis of MCC will likely improve. With the expansion of colon cancer screening, the incidence of MCC is likely to rise, highlighting the importance of timely, accurate diagnosis when facing poorly-differentiated colonic tumors.