IDRX-42 (formerly M4205) is a highly selective small molecule KIT inhibitor compound developed for the treatment of gastrointestinal stromal tumors. The compound was originally discovered by the German company Merck and later out-licensed to IDRX. In November 2024, promising anti-tumor data from ongoing Phase 1/1B studies were reported. In January 2025, the compound played a key role in the $1 billion acquisition of IDRX by GSK.
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