Neoplasia USMLE Step 1 Practice Question
A 68-year-old man presents with a 3-month history of bloody diarrhea and weight loss. Colonoscopy reveals a 4-cm mass in the sigmoid colon; biopsy confirms adenocarcinoma. A tumor cell line derived from this specimen divides indefinitely in culture without entering replicative senescence, despite normal p53 function. The cells maintain telomere length through continuous proliferation. There is no evidence of apoptosis. Which of the following molecular changes most directly explains this capability?
Answer choices
- AInhibition of cyclin D
- BIncreased mismatch repair fidelity
- CLoss of angiogenic potential
- DTelomerase activation allowing limitless replicationCorrect answer
- EEnhanced apoptosis through caspase activation
- FInactivation of retinoblastoma (Rb) protein through phosphorylation
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