Primary medullary adenocarcinoma of the colon: Literature review and case series

Abstract

Aims: Medullary carcinoma of the colon is a rare subtype of adenocarcinoma, first described in 1999. Clinically known to have a favorably prognosis in comparison to poorly differentiated cancers, it is invariably associated with mismatch gene repair. This is an observational study of Hobart’s patient population with medullary cancer, and compares data with the current literature. Methods: We performed a search of the pathological database at our institution for medullary adenocarcinomas between the years of 2016 and 2023 and reviewed their clinical information to collect all relevant data including patient history, hospital admissions, surgery and clinic visits. We then performed a literature search using PubMed for search terms medullary cancer/carcinoma of the colon/colorectum. Results: Eleven patients were found in our database, 34 papers in the literature (19 retrospective cohort studies and 13 case reports). 81.8% (vs. 73.22% in cohort studies) were females. 8/11 patients had lymphovascular invasion (LVI) with 2/11 patients had perineural involvement (PNI). The immunohistochemistry (IHC) results showed that in all (11/11) patients’ tumors, there was a loss of MLH1 and PMS2 proteins, while MSH2 and MSH6 proteins were present. Cohort studies demonstrated 302/1897 (15.92%) patients had perineural invasion (PNI) with 1133/2151 (52.67%) demonstrating LVI. MLH1 testing was available for 192 patients, with 93.75% having loss of MLH1. Conclusion: Our cohort of medullary cancer patients was similar to that in the literature, with regard to demographic, staging, and tumor characteristics. A longer follow-up time is required for our cohort to produce comparable survival outcomes.