Table 1.
World Health Organization (WHO) classification of Systemic Mastocytosis.
| DIAGNOSTIC CRITERIA | B FINDING III | C FINDING IV | |
|---|---|---|---|
| ONE MAJOR I CRITERIA AND ONE MINOR II OR THREE MINORS | |||
| BMM | YES | ˂2 | NO |
| ISM | YES | ˂2 | NO |
| SSM | YES | ≥2 | NO |
| ASM | YES | ≥1 | |
| SM—AHN | YES | ASSOCIATED HEMATOLOGIC NEOPLASM (non MC-lineage) |
|
| MCL | ≥20% MAST CELL IN BONE MARROW SMEAR |
BMM: bone marrow mastocytosis; ISM: indolent systemic mastocytosis; SSM: smoldering systemic mastocytosis; ASM: aggressive systemic mastocytosis; SM-AHN: systemic mastocytosis with an associated hematological neoplasm; MCL: mast cell leukemia; MC: mast cell; BM: bone marrow. I. Major criteria: histological finding of at least 15 multifocal dense MC infiltrates in BM or other extracutaneous organs. II. Minor criteria: i. Abnormal morphology of extracutaneous MCs; ii. Serum tryptase >20 ng/mL; iii. Expression of CD2 and/or CD25 on MCs in BM or other extracutaneous organs; iv. Detection of a mutation at codon 816 of the KIT gene in BM, blood or extracutaneous organs. III. B findings: i. BM biopsy: >30% infiltration of cellularity by MCs (focal, dense aggregates) and serum total tryptase level >200 ng/mL; ii. Signs of dysplasia or myeloproliferation, in non-MC lineage(s), but insufficient criteria for definitive diagnosis of an associated hematological neoplasm (AHN), with normal or only slightly abnormal blood counts; iii. Hepatomegaly without impairment of liver function, palpable splenomegaly without hypersplenism, and/or lymphadenopathy on palpation or imaging. IV. C findings: i. BM dysfunction caused by neoplastic MC infiltration, manifested by ≥1 cytopenia(s) (ANC < 1.0 × 109/L, Hgb < 10 g/dL, platelet count < 100 × 109/L); ii. Palpable hepatomegaly with impairment of liver function, ascites, and/or portal hypertension; iii. Skeletal involvement with large osteolytic lesions with/without pathological fractures (pathological fractures caused by osteoporosis do not qualify as a “C” finding); iv. Palpable splenomegaly with hypersplenism. v. Malabsorption with weight loss due to gastrointestinal mast cell infiltrates.