Diagnosis: Chronic myelomonocytic leukemia
• Presence of a PDGFRA or PDGFRB abnormality is an exclusion criterion for chronic myelomonocyic leukemia (CMML). CMML with eosinophilia commonly has a PDGFRB abnormality. PDGFRB abnormalities constitute translocations involving the 5q31~33 locus, the most common of which being t(5;12)(q31~q33;p12).
• Myeloid and lymphoid neoplasms with eosinophilia associated with a PDGFRA or PDGFRB abnormality were separately designated because these patients were responsive to imatinib (Gleevac). Persistent peripheral blood monocytosis is required for the diagnosis of CMML (A).
• Reactive causes of monocytosis must be ruled out. Persistent monocytosis is typically seen for at least three months. CMML is one of the overlapping myelodysplastic/myeloproliferative neoplasms (MPN) and is characterized by increased blood counts and variable degrees of dysplasia (B).
• Dysplasia is seen in one or more lineages in CMML. If dysplasia is not present and a clonal cytogenetic or molecular abnormality is present, a diagnosis of CMML can still be made.
• The most common cytogenetic abnormalities in CMML are trisomy 8 and monosomy 7. Ras gene mutations are also common in CMML.
• If 20% or more are blasts or promonocytes (promonocytes are blast equivalents) (C), then a diagnosis of an acute myeloid or acute myelomonocytic leukemia should be made.
• The presence of a Philadelphia chromosome or bcr-abl rearrangement (E) is indicative of chronic myeloid leukemia in the appropriate morphologic and immunophenotypic setting.
