The most likely diagnosis is serrated polyposis syndrome. Serrated polyposis syndrome (SPS) is a familial polyposis syndrome without a known genetic cause. It is diagnosed by the World Health Organization criteria of (1) five or more serrated polyps proximal to the sigmoid colon, two or more of which are 10 mm in diameter or greater, (2) any number of serrated polyps proximal to the sigmoid colon in an individual with a first-degree relative who has SPS, or (3) more than 20 serrated polyps distributed throughout the colon. This patient has had six serrated polyps, two of which are larger than 10 mm; therefore, she meets criteria for SPS. SPS is associated with an increased risk of colorectal but not extraintestinal cancer. The mean age of colon cancer diagnosis is 56 years, and metachronous colon cancer occurs in 7% of patients at 5 years of follow-up. Because of this, patients with SPS should undergo colonoscopy yearly. Serrated polyps are a common finding on screening colonoscopy. It is important to recognize that hyperplastic polyps are the most common type of serrated polyp and, when small and located in the rectosigmoid colon, are believed to impart no risk to the patient. However, the other two forms of serrated polyps, sessile serrated polyps and traditional serrated adenomas, are precancerous lesions that occur in 3% and less than 1%, respectively, of individuals undergoing screening colonoscopy. Approximately 30% of colon cancers develop from sessile serrated polyps. Patients with neoplastic serrated polyps should undergo colonoscopy at an interval based on the size and pathology of the lesion.

Familial adenomatous polyposis (FAP) is characterized by tens to thousands of adenomatous colorectal polyps. This patient has no adenomatous polyps and, therefore, FAP is not the most likely diagnosis.

Lynch syndrome is a hereditary colon cancer syndrome caused by a germline mutation in a mismatch repair gene. Colorectal cancers in Lynch syndrome arise from adenomatous polyps. Although patients with Lynch syndrome can have numerous adenomatous polyps, it does not appear typically as a polyposis syndrome.

Peutz-Jeghers syndrome (PJS) is an autosomal dominant hamartomatous polyposis syndrome. The intestinal polyps in PJS are hamartomatous rather than serrated, as was seen in this patient.