Which statement best describes the mechanism by which trastuzumab (Herceptin) enhances chemotherapy efficacy in HER2-positive breast cancer?
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A
It directly alkylates DNA in HER2-overexpressing cells, acting as a targeted chemotherapy
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B
It binds the extracellular domain IV of HER2, blocking downstream PI3K/AKT and MAPK signaling while recruiting immune effectors via ADCC
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C
It inhibits HER2 kinase activity by competing with ATP at the intracellular binding domain
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D
It prevents HER2 dimerization by binding the extracellular domain II, functioning identically to pertuzumab