Crizotinib targets which mutation?

• A. ALK mutation
• B. HER2 mutation
• C. ER mutation
• D. RET mutation

Answer: (A)

Crizotinib is a tyrosine kinase inhibitor that targets ALK-driven cancers. It binds to the ALK kinase when it’s abnormally activated by gene rearrangements (such as EML4-ALK), blocking the ATP-binding site and shutting down signaling needed for tumor cell survival and proliferation. This makes it effective in ALK-positive tumors. It also has activity against ROS1 and MET, which is why it’s used for ROS1-rearranged cases as well. The other mutations listed—HER2, ER, and RET—are targeted by different therapies, not primarily by crizotinib (HER2 with HER2-directed treatments, ER with endocrine therapy, RET with selective RET inhibitors). So the mutation crizotinib most directly targets is ALK.