WBR0247
| Author | [[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pathology |
| Sub Category | SubCategory::Gastrointestinal |
| Prompt | [[Prompt::A 45-year-old male patient, whose father had colon cancer at the age of 55, presents to the physician's office for an annual checkup. You recommend that he undergoes a screening colonoscopy, 10 years prior to the age his father had colon cancer. You explain that most cases of colon cancer are sporadic, while some are familial and are related to gene mutations. A mutation in which of the following genes is most likely associated with familial colon cancer?]] |
| Answer A | AnswerA::C-kit |
| Answer A Explanation | [[AnswerAExp::The C-kit oncogene is associated with GIST.]] |
| Answer B | AnswerB::Ret |
| Answer B Explanation | [[AnswerBExp::The Ret oncogene is associated with MEN syndrome, type IIa and IIb.]] |
| Answer C | AnswerC::Abl |
| Answer C Explanation | [[AnswerCExp::The Abl oncogene is associated with CML.]] |
| Answer D | AnswerD::Ras |
| Answer D Explanation | [[AnswerDExp::The Ras oncogene is associated with colon carcinoma.]] |
| Answer E | AnswerE::C-myc |
| Answer E Explanation | [[AnswerEExp::The C-myc is associated with Burkitt's lymphoma.]] |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Familial adenomatosis polyposis (FAP) is an inherited condition, with an autosomal dominant mutation of the APC gene on chromosome 5q. FAP is often characterized by the excessive growth of polyps, which progresses to colon cancer in affected individuals. Carcinogenesis of FAP is based on a two-hit hypothesis that transforms the normal mucosa through an “adenoma-to-carcinoma” sequence.
The first step of the two-hit hypothesis involves a mutation of the tumor suppressor gene, APC. Loss-of-function mutations in APC can cause a reduction of intercellular adhesion, leading to a small polyp. Then, a mutation in K-ras, a GTPase, causes an uncontrolled intracellular signal transduction, stimulating cell growth, leading to an increase in the polyp size. Further loss of the tumor suppressor genes p53 and DCC, attribute to the transformation of an adenoma into a carcinoma. |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |