What is the hallmark feature and consequence of APC mutations in FAP?

What is the hallmark feature and consequence of APC mutations in FAP?

• A. Hundreds to thousands of polyps with near-certain risk of colorectal cancer; colectomy often required.
• B. A single polyp with low cancer risk.
• C. No polyps but high stomach cancer risk.
• D. Brain tumor predisposition.

Answer: (A)

Germline loss-of-function mutations in APC drive familial adenomatous polyposis by dysregulating the Wnt/beta-catenin pathway, leading to widespread colorectal adenomas. The defining feature is an enormous burden of polyps—typically hundreds to thousands—appearing at a young age. Because so many polyps carry malignant potential, colorectal cancer almost inevitably develops if the colon isn’t removed, so colectomy or extensive surgical management is often required. This combination of extreme polyp burden and almost certain cancer risk is what makes this scenario the best description of APC-mutant FAP. Other scenarios don’t fit: a single polyp suggests a sporadic adenoma rather than FAP; no polyps would not explain the high cancer risk; a brain-tumor predisposition points to different syndromes, not APC/FAP; and a non-colon cancer–focused risk doesn’t match the pervasive colorectal polyposis seen in FAP.

Germline loss-of-function mutations in APC drive familial adenomatous polyposis by dysregulating the Wnt/beta-catenin pathway, leading to widespread colorectal adenomas. The defining feature is an enormous burden of polyps—typically hundreds to thousands—appearing at a young age. Because so many polyps carry malignant potential, colorectal cancer almost inevitably develops if the colon isn’t removed, so colectomy or extensive surgical management is often required. This combination of extreme polyp burden and almost certain cancer risk is what makes this scenario the best description of APC-mutant FAP.

Other scenarios don’t fit: a single polyp suggests a sporadic adenoma rather than FAP; no polyps would not explain the high cancer risk; a brain-tumor predisposition points to different syndromes, not APC/FAP; and a non-colon cancer–focused risk doesn’t match the pervasive colorectal polyposis seen in FAP.