WBR0247
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pathology |
| Sub Category | SubCategory::Gastrointestinal |
| Prompt | [[Prompt::A 45 year old male patient, known to have a positive family history of colon cancer in his father at the age of 55, presents to his general practitioner for an annual checkup. His physician informs him that it is recommended that he undergoes a screening colonoscopy 10 years prior to the age his father had colon cancer. The patient asks the physisican about the etiology of colon cancer. His physician answers that most cases of colon cancer are sporadic while some are familial and they are related to mutations in some genes. Mutation in which of the following genes is associated with familial colon cancer?]] |
| Answer A | AnswerA::C-kit |
| Answer A Explanation | [[AnswerAExp::C-kit oncogene is associated with GIST.]] |
| Answer B | AnswerB::Ret |
| Answer B Explanation | [[AnswerBExp::Ret oncogene is associated with MEN syndrome type IIa and IIb.]] |
| Answer C | AnswerC::Abl |
| Answer C Explanation | [[AnswerCExp::Abl oncogene is associated with CML.]] |
| Answer D | AnswerD::Ras |
| Answer D Explanation | [[AnswerDExp::Ras oncogene is associated with colon carcinoma.]] |
| Answer E | AnswerE::C-myc |
| Answer E Explanation | [[AnswerEExp::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. It is characterized by early excessive growth of polyps that progress to colon cancer in 100% of affected individuals. The pathogenesis of FAP has been extensively studied. Tumorogenesis of FAP is based on a two-hit hypothesis that will transform the normal mucosa by an “adenoma-to-carcinoma” sequence.
The first step of the two-hit hypothesis involves a mutation of the tumor suppressor gene APC. Loss of APC will cause a reduction of intercellular adhesion leading to the progression to a small polyp. Then, a mutation of K-ras, a GTPase, causes an increased uncontrolled intracellular signal transduction stimulating cell growth causing an increase in the polyp size. Further loss of the tumor suppressor genes p53 and DCC attribute to the malignant transformation from an adenoma into a carcinoma. Educational objective: Mutation in K-ras oncogene is implicated in colon cancer. |
| Approved | Approved::No |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |