**Question:** Drug of choice for chronic myeloid Leukemia (CML) is:

A. Imatinib
B. Hydroxyurea
C. Cytarabine
D. Vincristine

**Core Concept:**
Chronic myeloid leukemia (CML) is a type of cancer that affects the white blood cells in the bone marrow. It is characterized by the presence of an abnormal chromosome called the Philadelphia chromosome (Ph chromosome), which results from the fusion of chromosomes 9 and 22 (t(9;22)). This fusion leads to the production of a protein called BCR-ABL, which is a tyrosine kinase enzyme that causes uncontrolled cell division and proliferation of white blood cells, leading to the development of CML.

**Why the Correct Answer is Right:**
The correct answer, Imatinib (Gleevec), is a tyrosine kinase inhibitor (TKI) that specifically targets the BCR-ABL enzyme. By inhibiting this enzyme, Imatinib helps to control the uncontrolled cell division and proliferation of white blood cells in CML patients, leading to improved disease control and overall survival. Imatinib has become the first-line treatment for CML due to its high efficacy, low toxicity, and manageable side effects.

**Why Each Wrong Option is Incorrect:**

B. Hydroxyurea (HU) is a chemotherapeutic agent primarily used for myeloproliferative disorders like polycythemia vera and sickle cell anemia, not CML. Although HU can be used in some CML cases, it is not the first-line treatment due to its inefficacy and higher toxicity compared to TKIs like Imatinib.

C. Cytarabine (Ara-C) is an antineoplastic agent primarily used in acute myeloid leukemia (AML) to induce remission. It is not the preferred treatment for CML due to its limited efficacy and higher toxicity compared to TKIs like Imatinib.

D. Vincristine (VCR) is a chemotherapeutic agent primarily used in acute lymphoblastic leukemia (ALL) and lymphomas. It is not the preferred treatment for CML due to its limited efficacy, high toxicity, and lack of targeting BCR-ABL enzyme, unlike Imatinib.

**Clinical Pearl:**
Gleevec (Imatinib) revolutionized the treatment of chronic myeloid leukemia (CML) by specifically targeting the BCR-ABL kinase, which is crucial for the management of CML patients. This targeted therapy has significantly improved the prognosis and overall survival of CML patients compared to traditional chemotherapy agents like Hydroxyurea, Cytarabine, and Vincristine.