A 25-year-old man is discovered to have colon cancer. It is noted that several members of his family also developed colon cancer at relatively young ages. Which of the following genes is most likely to be involved
**Core Concept**
The question is testing the association between familial colon cancer and specific genetic mutations. The underlying principle involves the identification of a tumor suppressor gene that, when mutated, increases the risk of developing colon cancer.
**Why the Correct Answer is Right**
The correct answer involves the APC gene, which is a tumor suppressor gene that plays a crucial role in the Wnt signaling pathway. Mutations in the APC gene lead to the accumulation of β-catenin in the nucleus, resulting in the activation of target genes involved in cell proliferation and survival. This ultimately contributes to the development of colorectal cancer, particularly in familial adenomatous polyposis (FAP) syndrome.
**Why Each Wrong Option is Incorrect**
**Option A:** The KRAS gene is involved in the MAPK signaling pathway and is a common mutation in various cancers, including colorectal cancer. However, it is not the primary gene associated with familial colon cancer.
**Option B:** The TP53 gene is a tumor suppressor gene involved in DNA repair and cell cycle regulation. While TP53 mutations are associated with Li-Fraumeni syndrome and increased cancer risk, they are not specifically linked to familial colon cancer.
**Option C:** The SMAD4 gene is involved in the TGF-β signaling pathway and is a tumor suppressor gene. Mutations in SMAD4 are associated with juvenile polyposis syndrome and increased colon cancer risk, but it is not the primary gene associated with familial colon cancer.
**Clinical Pearl / High-Yield Fact**
Familial adenomatous polyposis (FAP) syndrome is characterized by the development of hundreds to thousands of adenomatous polyps in the colon and rectum, which have a high risk of progressing to colorectal cancer if left untreated. Regular screening and prophylactic colectomy are essential for preventing cancer in individuals with FAP.
**Correct Answer:** C. SMAD4