**Core Concept:** Tumor suppressor genes play a crucial role in preventing uncontrolled cell growth and maintaining genomic stability. They are often mutated in cancers, leading to uncontrolled cell growth and a higher risk of malignant tumors. Chromosome locations for some tumor suppressor genes include:

- DCC gene (deleted in colorectal cancer) is located on chromosome 18q21.1. It is a tumor suppressor gene involved in the regulation of cell adhesion and apoptosis.
- TP53 gene (tumor protein p53) is located on chromosome 17p13.1 and encodes a protein that regulates cell cycle progression, DNA repair, and apoptosis. Mutations in TP53 are associated with a wide range of cancers, including colorectal, pancreatic, and ovarian cancers.
- APC gene (adenomatous polyposis coli) is located on chromosome 5q21 and is involved in the regulation of cell growth and differentiation, particularly in colorectal cancers.
- SMAD4 gene (SMAD family member 4) is located on chromosome 18q21.1 and plays a role in the TGF-beta signaling pathway, regulating cell growth, differentiation, and apoptosis. Mutations in SMAD4 are associated with juvenile polyposis syndrome and colorectal cancer.

**Question:** A patient complains to a physician of epigastric pain that fails to respond to antacids. Endoscopy demonstrates an ulcerated mass on the greater curvature of the stomach. Genetic studies on the tumor demonstrate an altered DCC gene. Which of the following tumor suppressor genes is found on the same chromosome as DCC?

**Answer:**

**Core Concept:** The question asks about a tumor suppressor gene found on the same chromosome as DCC. DCC gene is located on chromosome 18q21.1. The correct answer is:

**Correct Answer:** SMAD4 gene (located on chromosome 18q21.1) is found on the same chromosome as DCC. SMAD4 is part of the TGF-beta signaling pathway, regulating cell growth, differentiation, and apoptosis. Mutations in SMAD4 are associated with juvenile polyposis syndrome and colorectal cancer.

**Why the Correct Answer is Right:** SMAD4 is the correct answer because both DCC and SMAD4 are involved in the TGF-beta signaling pathway, which plays a crucial role in regulating cell growth, differentiation, and apoptosis. Mutations in SMAD4 are associated with juvenile polyposis syndrome and colorectal cancer, which are conditions involving gastrointestinal tract lesions and cancer.

**Why Other Options are Incorrect:**

**Option A (DCC):**

The DCC gene is involved in the Wnt signaling pathway, not the TGF-beta pathway. Mutations in DCC are associated with neurofibromatosis type 2 and schwannomas, not gastrointestinal tract lesions and cancer.

**Option B (TP53):**

The TP53 gene is located on chromosome 17p13.1, which is different from chromosome 18q21.1 (where SMAD4 is located). Mutations in TP53 are associated with Li