## Epidemiology of Chronic Leukemias **Key Point:** Chronic myeloid leukemia (CML) is the most common chronic leukemia in adults, accounting for 15–20% of all leukemias in developed countries and up to 25% in India. ### Diagnostic Features of CML | Feature | CML | |---------|-----| | **Cytogenetic hallmark** | t(9;22) Philadelphia chromosome (BCR-ABL fusion) | | **Median age at diagnosis** | 50–60 years | | **Splenomegaly** | Present in 50% of cases | | **WBC count** | Often markedly elevated (>100,000/μL) | | **Bone marrow** | Hypercellular with myeloid predominance | | **Prognosis (pre-TKI era)** | Median survival ~3–5 years | ### Chronic Leukemia Frequency Ranking 1. **Chronic myeloid leukemia** — 40–50% of chronic leukemias 2. **Chronic lymphocytic leukemia** — 30–40% of chronic leukemias (more common in Western populations) 3. **Chronic neutrophilic leukemia** — <5% of chronic leukemias 4. **Chronic eosinophilic leukemia** — Rare, often associated with FIP1L1-PDGFRA **High-Yield:** The presence of t(9;22) (Philadelphia chromosome) is pathognomonic for CML and is present in >95% of cases. The BCR-ABL fusion protein has constitutive tyrosine kinase activity, driving uncontrolled myeloid proliferation. **Clinical Pearl:** In India, CML represents a significant proportion of hematologic malignancies due to delayed diagnosis and presentation in advanced disease stages. Early recognition via cytogenetics or BCR-ABL PCR is critical for initiating tyrosine kinase inhibitor (TKI) therapy. **Mnemonic: CML = Common Myeloid Leukemia** — remember it as the most frequent chronic leukemia in adults globally.
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