Colorectal polyps and cancer
In classic FAP extensive colonic adenomatous polyposis is typically evident early in the second decade of life (but can develop earlier). In atypical FAP polyps typically develop at a later age, although the age at first polyps varies from adolescence to mid-to-late adulthood. Without polypectomy and/or colectomy polyps eventually become malignant. CRC occurs most often in adulthood but is occasionally seen in childhood or adolescence.
Multiple studies have demonstrated that surveillance colonoscopy from early childhood with appropriately timed colectomy reduces CRC incidence and mortality.r The natural history of polyposis supports annual surveillance in classical FAP. It also supports surveillance by either sigmoidoscopy or colonoscopy until polyps are first detected, and then by colonoscopy.r
Some experts recommend less frequent (2-3 yearly) colonoscopy for individuals at risk of atypical FAP who have not developed polyps. They recommend an increase to 1-2 yearly colonoscopy once polyps have been detected, with the frequency guided by polyp burden.r Others recommend annual surveillance because of the variability in polyp phenotype that is seen both between and within families. In AFAP polyps have a more proximal colonic preponderance and colonoscopy should be used for surveillance (not sigmoidoscopy).
Gastric, duodenal and small bowel polyps and cancer
Gastric, duodenal and jejunal polyps may be evident by the second decade of life. Progression of gastric polyps to malignancy is uncommon.r However, 3-18% of FAP patients develop duodenal or periampullary cancers.rr The recommended upper gastrointestinal (GI) surveillance protocol is based on published literature and expert opinion.r
A 2021 historical cohort study including 49 patients with FAP who underwent an endoscopic duodenal intervention (139 duodenal polypectomies) between 2002 and 2018 showed duodenal surgery–free and duodenal cancer–free survival after polypectomy was 97% at 12 months, 86% at 24 months, and 74% at 89 months. Prophylactic duodenal polypectomies were relatively safe and effective.r
Thyroid cancer
A 2015 study prospectively screened 205 FAP patients with annual thyroid ultrasounds comparing outcomes with non-screen detected (NSD) thyroid cancers from the colon cancer registry database. The mean tumour size was larger in the NSD group than the screen-detected (SD) group (p=0.04), and they tended to demonstrate more positive lymph nodes and more complications than the SD group (however this was not statistically significant).r A 2011 study of thyroid screening in 192 patients detected thyroid cancer in 5 (2.6%) participants. Clinical history and neck exam did not detect any of the 5 cancers.r A recent 2019 study of 264 FAP patients showed that in patients with normal baseline thyroid ultrasound, it would be reasonable to extend the screening interval until nodules are detected.r
Desmoid-type fibromatosis
Although desmoid-type fibromatosis is a benign fibroblastic neoplasm, intra-abdominal desmoids can cause substantial morbidity in patients with FAP, and contribute to FAP-related mortality. Abdominal surgery, APC pathogenic variant site and positive family history for desmoid-type fibromatosis are consistent risk factors for development of desmoid-type fibromatosis.r There is conflicting evidence regarding female gender, pregnancy and oestrogen exposure. Some experts recommend annual surveillance using abdominopelvic MRI for patients who have had abdominal surgery and have a family history, but there is no evidence of benefit.
Other cancers
The American College of Gastroenterology recommends hepatoblastoma surveillance from birth to age 7 years. However, there is substantial controversy about surveillance as the absolute risk of hepatoblastoma is small and there is no evidence of benefit of surveillance.r