A 78-year-old man repos anorexia, fatigue, and generally feeling unwell. On examination he has a large spleen, appears pale, and the rest of the examination is normal. His blood count is abnormal; the WBC is 46000/ml with increased mature granulocytes, hemoglobin 9.0 g/dL, and platelets 450,000/mL. Fuher investigations reveal BCR-ABL transcripts. T315I mutation is also seen. What is the drug of choice for this condition?

**Core Concept**
The patient is diagnosed with Chronic Myeloid Leukemia (CML), a type of cancer characterized by the uncontrolled growth of myeloid cells due to a chromosomal abnormality known as the Philadelphia chromosome. This results from a reciprocal translocation between chromosomes 9 and 22, leading to the BCR-ABL fusion gene.

**Why the Correct Answer is Right**
The BCR-ABL fusion gene produces a constitutively active tyrosine kinase, which drives the proliferation of myeloid cells. The T315I mutation is a resistance mutation that confers resistance to tyrosine kinase inhibitors (TKIs). The drug of choice for CML with a T315I mutation is Ponatinib, a potent and selective TKI that can overcome this resistance. Ponatinib inhibits the BCR-ABL tyrosine kinase activity, leading to the inhibition of myeloid cell proliferation and apoptosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Imatinib is a first-generation TKI that is effective against CML, but it is not the drug of choice for patients with the T315I mutation. Imatinib can be used as a first-line treatment for CML without the T315I mutation.
**Option B:** Dasatinib is a second-generation TKI that is effective against CML, including some cases with the T315I mutation. However, it is not the preferred drug of choice for patients with this specific mutation.
**Option C:** Nilotinib is another second-generation TKI that is effective against CML, but it is not the preferred drug of choice for patients with the T315I mutation.

**Clinical Pearl / High-Yield Fact**
Ponatinib is a high-risk medication due to its potential for serious side effects, including arterial thromboembolic events and pancreatitis. It is essential to carefully weigh the benefits and risks of using Ponatinib in patients with CML and the T315I mutation.

**Correct Answer: C. Ponatinib**

✓ Correct Answer: B. Ponatinib