Medullary Carcinoma of the Colon and Rectum
Definition
- Poorly differentiated adenocarcinoma with regular nuclei and pushing border arising in the colon or rectum
Alternate/Historical names
- Large cell carcinoma with minimal differentiation
- Solid type poorly differentiated carcinoma
- Poorly differentiated carcinoma of medullary type
- Undifferentiated carcinoma solid pattern type
Diagnostic Criteria
- Solid sheets, nests and trabeculae
- No to rare gland formation
- Uniform small to medium sized cells
- Vesicular nuclei with prominent nucleoli
- High nuclear/cytoplasmic ratio
- Scant to moderate cytoplasm
- Eosinophilic to amphophilic
- Scant to moderate cytoplasm
- Pushing, expansive border
- Prominent lymphocytic infiltrate
- Intraepithelial lymphocytes, ≥3 per HPF
- Crohn-like response at edge of carcinoma
- Lymphoid aggregates / follicles with or without germinal centers not associated with a lymph node
- Neuroendocrine markers must be negative
- At most, focal or scattered staining
- May have intracytoplasmic mucin
- Mitotic figures may be frequent
- May have geographic or comedo necrosis
- Lacks dirty necrosis pattern
- 80% of neoplasm has distinctive features
- Up to 20% may range from well differentiated adenocarcinoma to mucinous carcinoma
- Almost always microsatellite unstable
- May be associated with Hereditary Non-polyposis Colon Cancer syndrome
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting/updates : 1/31/10, 11/12/11
