Medullary colorectal carcinoma

Medullary colorectal carcinoma is a rare type of colorectal carcinoma.

General

• Rare subtype of colorectal carcinoma.
• Typically has Microsatellite instability.
• Prognostic significance dependent on study.
  • A small series suggests the prognosis of medullary carcinoma with MSI is worse that conventional colorectal carcinoma without MSI.
  • A series with 102 cases suggests a better prognosis when compared on the basis of other pathological characteristics.

Gross

• Well-circumscribed.

Microscopic

Features:

• Poorly differentiated carcinoma:
  • Noninfiltrative border.
  • Solid pattern/nests.
  • No gland formation.
  • Lymphocytic infiltrate.

DDx:

• Other (poorly differentiated) colorectal carcinomas.
• Carcinomas with neuroendocrine differentiation.

IHC

Features:

• CDX2 +ve.
• Beta-catenin +ve.
• MLH1 loss of staining.

Note:

• CDX2, beta-catenin, MLH1 useful for differentiating from poorly differentiated colorectal carcinoma.

See also

• Colorectal adenocarcinoma.