Bone marrow biopsy of a patient with chronic myeloid leukemia shows 22% blasts and dysplastic features in two lineages. The BCR-ABL1 ratio (IS) is 35%. According to the WHO 2022 classification, how is this phase best classified?

• A Chronic phase CML
• B Accelerated phase CML
• C Mixed phenotype acute leukemia with BCR-ABL1
• D Blast phase CML — myeloid type ✓

Explanation

WHO 2022 (5th edition) revised the threshold for blast phase (BP) CML to ≥20% blasts in blood or bone marrow (eliminating the former 'accelerated phase' as a distinct WHO-defined entity). With 22% blasts, this fulfills blast-phase criteria. The WHO 2022 classification eliminates accelerated phase as a separate category and recognises only chronic phase and blast phase. Dysplasia in two lineages is a consequence of the leukemic transformation rather than a separate MDS. MPAL with BCR-ABL1 would require meeting MPAL immunophenotypic criteria.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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