The 2023 Updated Classification and Diagnostic Criteria of Mastocytosis

Abstract

Mastocytosis is an uncommon hematologic malignancy characterized by accumulation of abnormal mast cells in various organs or tissues. A somatic point mutation in the KIT gene at codon 816 is detected in more than 90% of patients with systemic Masto cytosis (SM). The 2022 WHO classification continues to recognize three disease types: systemic mastocytosis, cutaneous mastocytosis and mast cell sarcoma. Bone marrow mastocytosis is a new separate subtype of SM. The classification also recognizes well-differentiated systemic mastocytosis, a morphologic pattern that can occur in any SM subtype. Diagnostic criteria for SM have been modified. The expression of CD30 and the presence of any KIT mutation causing ligand-independent activation have been accepted as minor diagnostic criteria. Classical B-findings and C-findings have undergone minor refinements. Most notably, variant allele frequency of D816V mutation ≥ 10% in bone marrow cells or peripheral blood leukocytes is qualified as a B-finding.