Neoplasia and Cancer Biology · USMLE Step 1

Why are malignant neoplasms often genetically heterogeneous within the same tumor mass?

  1. Because they arise from multiple independent cells
  2. Because clonal evolution accumulates additional mutations over time
  3. Because benign tumors transform to malignant synchronously
  4. Because of uniform oncogene expression across all cells
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Correct answer: Because clonal evolution accumulates additional mutations over time

Genetic instability in cancer cells leads to accumulation of new mutations over time; clonal evolution produces subpopulations with diverse genetic profiles — accounting for intratumoral heterogeneity.

Difficulty: Medium Question 14 of 20

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