**Core Concept**
Imatinib is a targeted therapy drug that specifically inhibits certain tyrosine kinases, enzymes responsible for phosphorylation in signal transduction pathways. This mechanism is crucial in treating diseases characterized by uncontrolled cell growth and proliferation. Imatinib's efficacy in specific cancers is linked to its ability to block aberrant tyrosine kinase activity.

**Why the Correct Answer is Right**
Imatinib acts by selectively inhibiting tyrosine kinases, including BCR-ABL, c-KIT, and PDGFR. This inhibition disrupts the signaling pathways that promote cell proliferation and survival in various cancers. For instance, BCR-ABL is a fusion protein resulting from the Philadelphia chromosome abnormality in chronic myeloid leukemia (CML). By inhibiting BCR-ABL, imatinib effectively treats CML. Additionally, imatinib is used to treat gastrointestinal stromal tumors (GISTs), which arise from the interstitial cells of Cajal and are characterized by mutations in the c-KIT gene. Furthermore, pedal edema is a known side effect of imatinib, likely due to its effect on vascular endothelial growth factor receptor (VEGFR) signaling.

**Why Each Wrong Option is Incorrect**
**Option A:** While imatinib does inhibit tyrosine kinase, stating that it "acts by inhibition of tyrosine kinase" is too simplistic and doesn't capture the specificity of its action on particular tyrosine kinases.

**Option B:** Although imatinib is indeed used to treat GIST, this option doesn't acknowledge the other correct statements about imatinib's mechanism and side effects.

**Option C:** While pedal edema is a side effect of imatinib, this option doesn't mention the drug's mechanism of action or its use in treating GIST.

**Clinical Pearl / High-Yield Fact**
Imatinib's development highlights the importance of understanding the molecular basis of disease and targeting specific molecular defects for effective treatment. This approach has revolutionized the management of certain cancers and has paved the way for the development of other targeted therapies.

**Correct Answer Line**
✓ Correct Answer: D. All of the above.