The correct answer is:
C) Prophylactic colectomy
This patient has classic familial adenomatous polyposis (FAP), an autosomal dominant disorder caused by mutations in the APC tumor suppressor gene. The diagnosis is suggested by the presence of hundreds of adenomatous polyps during adolescence and a strong family history of early-onset colorectal cancer. The lifetime risk of colorectal cancer in untreated classic FAP approaches 100%, often by the fourth decade of life.
The APC gene normally regulates β-catenin signaling and suppresses cellular proliferation within the colonic epithelium. Loss of APC function results in uncontrolled adenoma formation throughout the colon. Because the number of polyps is so extensive, endoscopic surveillance alone cannot reliably prevent malignant transformation. Therefore, prophylactic colectomy is recommended once the diagnosis is established or when polyp burden becomes significant.
Step 2 frequently tests hereditary colorectal cancer syndromes. A key distinction is that FAP involves hundreds to thousands of adenomas and nearly universal progression to cancer without surgery. This contrasts with Lynch syndrome, which involves relatively few polyps but accelerated progression from adenoma to carcinoma due to defects in DNA mismatch repair.
Patients with FAP also require surveillance for extracolonic manifestations, including duodenal adenomas, desmoid tumors, osteomas, congenital hypertrophy of the retinal pigment epithelium, and thyroid cancer.
Answer choice A: Annual fecal immunochemical testing, is incorrect.
Fecal immunochemical testing (FIT) is used as a screening tool in average-risk populations. This patient already has confirmed FAP and an extremely high cancer risk. Stool-based screening is inadequate.
Answer choice B: Colonoscopy every 10 years, is incorrect.
Ten-year screening intervals are appropriate after a normal screening colonoscopy in average-risk adults. Patients with FAP require much more aggressive management because malignant transformation is nearly inevitable.
Answer choice D: Repeat colonoscopy in 5 years, is incorrect.
Although surveillance colonoscopy is important, it is insufficient as definitive management for classic FAP. The sheer number of polyps makes complete cancer prevention through endoscopic removal impractical.
Answer choice E: Surveillance only until age 50, is incorrect.
Cancer risk develops decades earlier in FAP. Waiting until age 50 would expose the patient to an extremely high likelihood of developing colorectal cancer.
Key Learning Point
Familial adenomatous polyposis is caused by APC mutations and is characterized by hundreds to thousands of adenomatous polyps. Prophylactic colectomy is required because the lifetime risk of colorectal cancer approaches 100%.
