Imatinib 400 mg tablets are a targeted cancer therapy, primarily used for Chronic Myeloid Leukemia (CML) and Gastrointestinal Stromal Tumors (GIST). A protein enzyme, bcr-abl tyrosine kinase, responsible for the growth of abnormal proliferation of cancer cells. This medicine inhibits the proliferation and induces apoptosis (planned cell death) in bcr-abl positive cells (cancer cells). This is how it works to stop or slow the spread of cancer.