Review of the Lynch syndrome: history, molecular genetics, screening, differential diagnosis, and medicolegal ramifications

TLDR

Lynch syndrome accounts for about 3 % of colorectal cancer cases, affecting over a million patients worldwide, and requires genetic counseling, mismatch repair gene testing, and regular colorectal cancer screening. Patients with Lynch syndrome undergo colonoscopy starting at age 25, repeated every 1–2 years until age 40 and annually thereafter, with subtotal colectomy considered if cancer develops, and tailored surveillance for associated extracolonic cancers such as endometrial, ovarian, and others. Lynch syndrome accounts for only 10–25 % of familial colorectal cancer cases.

Abstract

More than one million patients will manifest colorectal cancer (CRC) this year of which, conservatively, approximately 3% (∼30,700 cases) will have Lynch syndrome (LS), the most common hereditary CRC predisposing syndrome. Each case belongs to a family with clinical needs that require genetic counseling, DNA testing for mismatch repair genes (most frequently MLH1 or MSH2) and screening for CRC. Colonoscopy is mandated, given CRC's proximal occurrence (70–80% proximal to the splenic flexure). Due to its early age of onset (average 45 years of age), colonoscopy needs to start by age 25, and because of its accelerated carcinogenesis, it should be repeated every 1 to 2 years through age 40 and then annually thereafter. Should CRC occur, subtotal colectomy may be necessary, given the marked frequency of synchronous and metachronous CRC. Because 40–60% of female patients will manifest endometrial cancer, tailored management is essential. Additional extracolonic cancers include ovary, stomach, small bowel, pancreas, hepatobiliary tract, upper uroepithelial tract, brain (Turcot variant) and sebaceous adenomas/carcinomas (Muir‐Torre variant). LS explains only 10–25% of familial CRC.