F amilial adenomatous polyposis (FAP) is one of two well described forms of hereditary colorectal cancer. The primary cause of death from this syndrome is colorectal cancer which inevitably develops usually by the fifth decade of life. Screening by genetic testing and endoscopy in concert with prophylactic surgery has significantly improved the overall survival of FAP patients. However, less well appreciated by medical providers is the second leading cause of death in FAP, duodenal adenocarcinoma. This review will discuss the clinicopathological features, management, and prevention of duodenal neoplasia in patients with familial adenomatous polyposis.
FAMILIAL ADENOMATOUS POLYPOSISc FAP is an autosomal dominant disorder caused by a germline mutation in the adenomatous polyposis coli (APC) gene. FAP is characterised by the development of multiple (>100) adenomas in the colorectum. Colorectal polyposis develops by age 15 years in 50% and age 35 years in 95% of patients. The lifetime risk of colorectal carcinoma is virtually 100% if patients are not treated by colectomy.
1Patients with FAP can also develop a wide variety of extraintestinal findings. These include cutaneous lesions (lipomas, fibromas, and sebaceous and epidermoid cysts), desmoid tumours, osteomas, occult radio-opaque jaw lesions, dental abnormalities, congenital hypertrophy of the retinal pigment epithelium, and nasopharyngeal angiofibroma. In addition, FAP patients are at increased risk for several malignancies, such as hepatoblastoma, pancreatic, thyroid, biliary-tree, and brain tumours. Other gastrointestinal manifestations commonly found in FAP patients are duodenal adenomas, and gastric fundic gland and adenomatous polyps. Of concern, duodenal cancer is the second leading cause of death after colorectal cancer in these individuals.
EPIDEMIOLOGY OF DUODENAL POLYPS AND CANCERAfter the colorectum, the duodenum is the second most commonly affected site of polyp development in FAP (fig 1). 2 3 Duodenal adenomas can be found in 30-70% of FAP patients 2-4 and the lifetime risk of these lesions approaches 100%. 4 5 Duodenal/periampullary adenocarcinoma is the leading cause of death in FAP after colorectal cancer. 6 These patients have a 100-330-fold higher risk of duodenal cancer compared with the general population. 7 8 Of note, duodenal cancer is rare in the population, with an incidence of 0.01-0.04%. 9 Estimates of the cumulative risk of developing duodenal cancer in FAP range from 4% at age 70 years to 10% at age 60 years.10 11 Recently, a large prospective five nation study set the cumulative incidence rate of duodenal cancer at 4.5% by age 57 years. The median age of duodenal cancer development was 52 years (range 26-58).