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5 slides generated from the cancer page, with a quiz from the open benchmark and speaker notes that cite the sources. Arrow keys move between slides; Print gives one slide per page.
Medullary carcinoma is a very rare form of bowel cancer in which sheets of poorly formed cells are packed with immune cells; almost all cases are mismatch-repair deficient and it occurs mostly in older women on the right side. Despite its ugly appearance it does at least as well as ordinary bowel cancer, and because of its immune features it is a natural candidate for immunotherapy.
The WHO classification lists medullary carcinoma as a distinct colorectal adenocarcinoma type with solid sheets of poorly differentiated cells, vesicular nuclei and a prominent intraepithelial lymphocytic infiltrate, nearly always mismatch-repair deficient (Nagtegaal 2020). In SEER it was extremely rare (5 to 8 per 10,000 colon cancers), most common in the proximal colon, twice as common in women who presented at a lower stage with a trend to favourable prognosis, and no case was reliably identified in the rectum or appendix (International Journal of Oncology 2010). Loss of MLH1 and PMS2 was found in more than 80 percent of 18 cases, most were negative for CK7, CK20 and CDX2, and cadherin-17 and SATB2 were expressed in 89 percent, which matters when it presents as a carcinoma of unknown primary (Archives of Pathology 2014). In 105 cases the microenvironment showed strong interferon-gamma-induced immunoregulatory gene expression, including IDO-1, distinct from other microsatellite-unstable carcinomas (Modern Pathology 2016).
How it differs from its parent: it is the extreme of the mismatch-repair deficient, right-sided, immune-rich colon cancer that the MSI-high page describes, with a distinctive marker profile (CDX2-negative) that can mislead the pathologist.
| Setting | Approach | Guideline |
|---|---|---|
| All stages | Treated as MSI-high colorectal cancer by stage, with checkpoint inhibitors for mismatch-repair deficient disease. | not mapped |