Drug of choice for Chronic Myeloid Leukaemia is
## **Core Concept**
Chronic Myeloid Leukaemia (CML) is a type of cancer that affects the white blood cells and tends to progress slowly over time. It is characterized by the presence of a specific chromosomal abnormality known as the Philadelphia chromosome, which results from a translocation between chromosomes 9 and 22. This abnormality leads to the production of a constitutively active tyrosine kinase, BCR-ABL.
## **Why the Correct Answer is Right**
Imatinib mesylate is a **tyrosine kinase inhibitor** that specifically targets the BCR-ABL tyrosine kinase, which is the product of the Philadelphia chromosome abnormality. By inhibiting this enzyme, imatinib effectively blocks the proliferation signal in CML cells, thereby controlling the progression of the disease. Imatinib has been shown to induce significant cytogenetic and molecular responses in patients with CML, making it the first-line treatment for this condition.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Busulfan is a chemotherapy drug that was historically used to treat CML but has largely been replaced by more targeted therapies like imatinib due to its higher efficacy and better side effect profile.
- **Option B:** Hydroxyurea is another chemotherapeutic agent that can help control white blood cell counts in CML but does not target the underlying cause of the disease and is not as effective as imatinib in achieving long-term control or cure.
- **Option D:** Interferon-alpha was used in the treatment of CML before the advent of tyrosine kinase inhibitors. While it can induce cytogenetic responses, it is less effective and more toxic than imatinib.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **resistance to imatinib** can occur, often due to mutations in the BCR-ABL gene. In such cases, **second-generation tyrosine kinase inhibitors** like dasatinib and nilotinib, or **third-generation inhibitors** like ponatinib, may be used. Monitoring for BCR-ABL levels is crucial in managing CML.
## **Correct Answer:** C. Imatinib.