OBSOLETE: Classic mast cell leukemia

Classic mast cell leukemia (MCL) is an obsolete diagnostic subcategory that was previously used to describe a severe form of systemic mastocytosis characterized by the presence of 20% or more mast cells in bone marrow aspirate smears and/or 10% or more mast cells in peripheral blood. This designation has been retired from current classification systems, and the condition is now encompassed under the broader term 'mast cell leukemia' without the classic/variant distinction. Mast cell leukemia itself is an extremely rare and aggressive neoplasm of mast cells that primarily affects the bone marrow and blood, but can also involve the skin, liver, spleen, and gastrointestinal tract. Key clinical features include hepatosplenomegaly, cytopenias (low blood counts), bone pain, weight loss, and symptoms related to excessive mast cell mediator release such as flushing, hypotension, diarrhea, and anaphylaxis-like episodes. The disease carries a poor prognosis, with median survival historically measured in months. Treatment options include cytoreductive chemotherapy, tyrosine kinase inhibitors (such as midostaurin or avapritinib, particularly in cases harboring the KIT D816V mutation), and allogeneic hematopoietic stem cell transplantation in eligible patients. Because this Orphanet entry is marked as obsolete, patients and clinicians should refer to the current mast cell leukemia classification for up-to-date diagnostic criteria and management guidelines.

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