Radiation Oncology/Cancer Syndromes/FAP

Familial adenomatous polyposis (FAP) / Gardner Syndrome

Adenomatous polyposis coli (APC) gene (5q21) - gatekeeper (controls other downstream genes)
100% progress to carcinoma, most by age 30, often in teens. 100s-1000s of polyps. Other malignancies: thyroid, GB, adrenal. image

Gardner syndrome

After it has been found to be caused by APC, merged into familial adenomatous polyposis (FAP)
Colonic adenomatous polyps plus multiple osteomas (skull, mandible, long bones), epidermal cysts, fibromatosis (usually intraabdominal after surgery), fibromas, lipomas, impacted and supernumerary teeth, dental cysts, lymphoid polyps in small intestine and fundic gland polyps in stomach. 100% develop colon cancer. Other malignancies: periampullary, thyroid, adrenal.
Mutation in APC gene but has variable penetrance so not all extracolonic features are present.