A Case of Microsatellite Instability-High Colon Cancer in a Young Woman With Familial Adenomatous Polyposis

J Natl Compr Canc Netw. 2021 Dec;19(12):1377-1381. doi: 10.6004/jnccn.2021.7073.

Abstract

Two major molecular pathways of colorectal carcinogenesis, chromosomal instability (CIN) and microsatellite instability (MSI), are considered to be mutually exclusive. Distinguishing CIN from MSI-high tumors has considerable therapeutic implications, because patients with MSI-high tumors can derive considerable benefit from immune checkpoint inhibitors, and tumors that evolved through the CIN pathway do not respond to these agents. Familial adenomatous polyposis (FAP) is a genetic syndrome that is defined by a mutation in the APC gene and is thought to lead to carcinogenesis through the CIN pathway. Here, we report a case of a young woman with FAP who was treated for medulloblastoma as a child and developed advanced MSI-high colon cancer as a young adult. Her response to second-line immunotherapy enabled resection of her colon cancer, and she is free of disease >10 months after surgery. This case highlights the potential for overlap between the CIN and MSI carcinogenic pathways and associated therapeutic implications.

Publication types

  • Case Reports

MeSH terms

  • Adenomatous Polyposis Coli* / complications
  • Adenomatous Polyposis Coli* / genetics
  • Adenomatous Polyposis Coli* / surgery
  • Colonic Neoplasms* / genetics
  • Colonic Neoplasms* / surgery
  • Colorectal Neoplasms* / genetics
  • Female
  • Humans
  • Microsatellite Instability
  • Microsatellite Repeats
  • Mutation
  • Young Adult