**Core Concept**
Imatinib is a tyrosine kinase inhibitor that specifically targets the BCR-ABL fusion protein responsible for chronic myeloid leukemia (CML) and gastrointestinal stromal tumors (GISTs). It works by competitively inhibiting the ATP binding site of the tyrosine kinase, thereby preventing the activation of downstream signaling pathways.

**Why the Correct Answer is Right**
Imatinib's mechanism of action is based on its ability to bind to the ATP-binding site of BCR-ABL, a constitutively active tyrosine kinase that drives the proliferation of CML cells. By inhibiting this enzyme, imatinib prevents the phosphorylation of downstream targets, ultimately leading to cell cycle arrest and apoptosis. Imatinib also has activity against other tyrosine kinases, including c-KIT and PDGFR, which are involved in the pathogenesis of GISTs.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to imatinib's mechanism of action or its approved indications.
**Option B:** Imatinib is not primarily used to treat this condition; other treatments, such as chemotherapy or targeted therapies, may be more relevant.
**Option C:** This is a potential side effect of imatinib, but it is not the primary indication for its use.

**Clinical Pearl / High-Yield Fact**
Imatinib's success in treating CML is a prime example of the importance of targeted therapy in oncology. By specifically inhibiting the BCR-ABL tyrosine kinase, imatinib has revolutionized the treatment of this disease and has improved patient outcomes.

**Correct Answer:** C. Gastrointestinal stromal tumors (GISTs)