| Major criterion plus one minor criterion OR three minor criteria. Major criterion: - Multifocal, dense infiltrates of mast cells (≥15 mast cells in aggregates) detected in sections of bone marrow and/or other extracutaneous organ(s).
Minor criterion: - In biopsy sections of bone marrow or other extracutaneous organs, >25% of the mast cells in the infiltrate are spindle-shaped or have atypical morphology, or of all mast cells in bone marrow aspirate smears, >25% are immature or atypical.
- Detection of an activating point mutation at codon 816 of KIT in bone marrow, blood, or another extracutaneous organ.
- Mast cells in bone marrow, blood, or other extracutaneous organs express CD25, with or without CD2, in addition to normal mast cell markers.
- Serum total tryptase persistently exceeds 20 ng/mL (unless there is an associated clonal myeloid disorder, in which case this parameter is not valid).
| - Bone marrow biopsy showing >30% infiltration by mast cells (focal, dense aggregates) and/or serum total tryptase level >200 mg/mL.
- Signs of dysplasia or myeloproliferation in nonmast cell lineage(s) but insufficient criteria for definitive diagnosis of a hematopoietic neoplasm (SM-AHN) with normal or only slightly abnormal blood counts.
- Hepatomegaly without impairment of liver function, and/or palpable splenomegaly without hypersplenism, and/or lymphadenopathy on palpation or imaging.
| - Bone marrow dysfunction manifested by one or more cytopenia (ANC <1 × 109/L, Hb <10 g/dL, or platelets <100 × 109/L) but no obvious nonmast cell hematopoietic malignancy.
- Palpable hepatomegaly with impairment of liver function, ascites, and/or portal hypertension.
- Skeletal involvement with large osteolytic lesions and/or pathologic fractures.
- Palpable splenomegaly with hypersplenism.
- Malabsorption with weight loss due to gastrointestinal mast cell infiltrates.
| Bone marrow biopsy shows a diffuse infiltration, usually compact, by atypical, immature mast cells. Bone marrow aspirate smears show ≥20% mast cells. |
