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Primary Colonic Medullary Carcinoma With Exclusive Squamous Differentiation.
Irene Y Chen1, Jennifer J Findeis-Hosey1, Lisa Cannon2
1Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY, U.S.A.
Anticancer Research
|July 7, 2021
Summary
Medullary carcinoma of the colon with squamous differentiation is a rare finding. This case highlights the unrecognized differentiation plasticity in mismatch repair-deficient colorectal cancers.
Area of Science:
- Gastroenterology
- Oncology
- Pathology
Background:
- Medullary carcinoma (MC) is a rare colorectal adenocarcinoma (CRC) subtype.
- MC frequently exhibits mismatch repair (MMR) deficiency.
- Exclusive squamous differentiation in MC has not been previously reported.
Observation:
- A 68-year-old woman presented with a large ascending colon mass.
- Biopsy revealed squamoid morphology, concerning for squamous cell carcinoma (SCC).
- The tumor showed features of both MC and SCC, with diffuse p40 and CK5/6 positivity and MMR deficiency.
Findings:
- The tumor metastasized to the lung but not lymph nodes.
- Next-generation sequencing confirmed a BRAF V600E mutation.
- Testing of 64 MMR-deficient CRC cases revealed only one with focal CK5/6 expression and none with p40 positivity.
Implications:
- This case presents diagnostic challenges due to the unusual differentiation.
- It reveals unrecognized differentiation plasticity in medullary carcinoma.
- Understanding this plasticity is crucial for accurate diagnosis and treatment of colorectal cancers.
