Histologic Features Suggestive of Hereditary Nonpolyposis Colorectal Carcinoma (HNPCC)

 

Synonym: MSI-H histology

 

Histologic Feature	Finding
differentiation	poorly differentiated or undifferentiated
cell type	mucinous or signet ring cell
growth pattern	solid or medullary, cribriform
lymphoid infiltrate	prominent (see below)

 

A characteristic feature is a heavy lymphoid infiltrate that may be:

(1) peritumoral

(2) infiltrating the tumor

(3) as lymphoid aggregates with germinal centers ("Crohn-like" reaction)

 

Testing for microsatellite instability may be considered if 2 or more of these findings are present.

 

An HNPCC tumor may lack these findings, so testing for microsatellite instability should be considered if other clinical features are present.