The importance of genetics for timing and extent of surgery in inherited colorectal cancer syndromes.

Approximately 5% of colorectal cancers arise within an inherited colorectal cancer syndrome, with known underlying genetic etiologies. These syndromes increase the risk of colorectal and extracolonic cancers. Identification of a specific genetic pathogenic variant defines the syndrome, and quantifies the elevated risks compared to the general population. Thus, knowing and understanding the risks associated with each pathogenic variant allows for risk-stratification and a more individualized management strategy. These factors influence both the timing of surgery and the extent of colorectal surgery for patients with these syndromes. Familial Adenomatous Polyposis (FAP) is a dominantly inherited polyposis syndrome caused by pathogenic variant in the APC gene and results in a near 100% chance of developing colorectal cancer if not treated. There is a genotype-phenotype correlation in which the affected gene locus is associated with severity of polyposis and the risk of desmoid disease. Prophylactic surgery ranging from total abdominal colectomy or total proctocolectomy is recommended before cancer develops. Lynch syndrome is a non-polyposis inherited syndrome caused by a pathogenic variant in MLH1, MSH2, MSH6, or PMS2. Although prophylactic colectomy in Lynch syndrome is uncommon, total abdominal colectomy as prophylaxis in the setting of colon cancer is recommended due to the likelihood of metachronous colorectal cancer. This article reviews the role of genetics surgical decision making with respect to the timing and extent of surgery within the hereditary colorectal cancer syndromes.