Table 1.

Criteria for diagnosis and definition of major clinical variants in systemic Mastocytosis (SM) (WHO, 2008; updated in 2016).⁵

Major criterion: Multifocal, dense infiltrates of MC (15 or more MC in aggregates) detected in section of BM and/or other extracutaneous organ(s) and confirmed by tryptase immunohistochemistry or other special stains

Minor criteria: In biopsy sections of BM or other extracutaneous organs, more than 25% of MC in the infiltrate are spindle-shaped or have atypical morphology or, of all MC in BM aspirate smears, more than 25% are immature or atypical MC. Detection of KIT point mutation at codon 816 in BM, blood or other extracutaneous organ(s) Co-expression of CD25 and/or CD2 on MC in BM, blood or other extracutaneous organ(s) Serum total tryptase persistently > 20 ng/ml (if there is an associated myeloid neoplasia this criterion isn’t valid)

B findings: > 30% infiltration of cellularity by MC (focal, dense aggregates) in BM biopsy and serum total tryptase >200 ng/ml Myeloproliferation or signs of dysplasia but criteria are not met for definitive diagnosis of an associated haematological neoplasms, no prominent cytopenias; Hepatomegaly and/or splenomegaly on palpation without impairment of organ function and/or lymphadenopathy on palpation/imaging (> 2 cm)

C findings: BM disfunctyons caused by neoplastic MC infiltration manifested by 1 ore more cytopenia: ANC < 1 × 109/L, Hb < 10 g/dL, or platelets < 100 × 109/L without other haematological neoplasms Hepatomegaly on palpation with impairment of liver function, ascites, and/or portal hypertension Skeletal lesions: osteolyses and/or pathologic fractures Palpable splenomegaly with hypersplenism Malabsorption with weight loss from gastrointestinal tract MC infiltrates

Legend: MC: mast cells. BM: bone marrow; ANC: absolute neutrophils count.