(Hereditary Nonpolyposis Colorectal Carcinoma; HNPCC)
Lynch syndrome is an autosomal dominant disorder in which patients with one of several known genetic mutations that impair DNA mismatch repair have a 70 to 80% lifetime risk of developing colorectal cancer (CRC). Compared to sporadic forms of colon cancer, Lynch syndrome occurs at a younger age (mid 40s), and the lesion is more likely to be proximal to the splenic flexure. The precursor lesion is usually a single colonic adenoma, unlike the multiple adenomas present in patients with familial adenomatous polyposis, the other main hereditary form of CRC.
However, similar to familial adenomatous polyposis, numerous extracolonic manifestations occur. Nonmalignant disorders include café-au-lait spots and sebaceous gland tumors. The low-grade skin cancer, keratoacanthoma, can occur. Other common associated cancers include endometrial tumors and ovarian tumors (39% risk of endometrial and 9% risk of ovarian by age 70). Patients also have an elevated risk of other cancers, including of the stomach, urinary tract, pancreas, biliary tree, gallbladder, small bowel, and brain.
(See also the 2015 American Gastroenterological Association's guideline regarding diagnosis and management of Lynch syndrome and the American College of Gastroenterology's clinical guideline on the genetic testing and management of hereditary gastrointestinal cancer syndromes.)
The specific diagnosis of Lynch syndrome is confirmed by genetic testing. However, deciding who to test is difficult because, unlike familial adenomatous polyposis, there is no typical phenotypic appearance. Thus, suspicion of Lynch syndrome requires a detailed family history, which should be obtained in all younger patients identified with colorectal cancer (CRC).
To meet the Amsterdam II criteria for Lynch syndrome, all three of the following historical elements must be present:
Patients meeting these criteria should have their tumor tissue tested either for MSI or with IHC to detect proteins responsible for DNA mismatch repair; however, most commercial and hospital pathology laboratories now routinely do this test on all colorectal adenocarcinoma specimens. The 2015 American Gastroenterological Association guidelines recommend that tumors of all patients with CRC should be tested either with IHC or for MSI. If MSI or IHC is positive, genetic testing for specific Lynch syndrome mutations is indicated.
Patients with Lynch syndrome should have a surveillance colonoscopy every 1 to 2 years. Patients with confirmed Lynch syndrome require ongoing screening for other cancers. For endometrial cancer, annual endometrial aspiration or transvaginal ultrasound is recommended. For ovarian cancer, options include annual transvaginal ultrasound and serum CA 125 levels. Prophylactic hysterectomy and oophorectomy are also options. Urinalysis may be used to screen for renal tumors.
First-degree relatives of patients with Lynch syndrome should have genetic testing. If no genetic testing has been done, they should have colonoscopy every 1 to 2 years beginning in their 20s, and annually after age 40. Female 1st-degree relatives should be tested annually for endometrial and ovarian cancer.
1. Umar A, Boland CR, Terdiman JP, et al: Revised Bethesda guidelines for hereditary nonpolyposis colorectal cancer (Lynch syndrome) and microsatellite instability. J Natl Cancer Inst 96(4):261–268, 2004.
The most common treatment of Lynch syndrome is resection of the index lesion with frequent surveillance for another colon cancer and any associated tumors in other organs. Because most Lynch syndrome tumors occur proximal to the splenic flexure, subtotal colectomy, leaving the rectosigmoid intact, has been suggested as an alternative. In either case, close follow-up is needed.
Certain autosomal dominant mutations confer a 70 to 80% lifetime risk of developing colorectal cancer.
Patients also have an increased risk of other cancers, particularly of the endometrium and ovary.
Symptoms, initial diagnosis, and treatment are similar to other forms of colorectal cancer.
Patients with certain familial risk factors should have their tumor tissue tested for microsatellite instability or with immunohistochemistry; if positive, genetic testing is done.
First-degree relatives who have not undergone genetic testing should have colonoscopy every 1 to 2 years beginning in their 20s, and annually after age 40; women should also be tested annually for endometrial and ovarian cancer.
Guidelines from the American Gastroenterological Association regarding the diagnosis and management of Lynch syndrome
Guidelines from the American College of Gastroenterology regarding the genetic testing and management of hereditary gastrointestinal cancer syndromes
Prediction Model for MLH1, MSH2, and MSH6 Gene Mutations (PREMM model)