Systemic mastocytosis: diagnostic criteria
| Major criterion • Multifocal dense infiltrates of tryptase- and/or CD117 positive mast cells (≥15 mast cells in aggregates) detected in sections of bone marrow and/or other extracutaneous organ(s)* |
| In the absence of the major criterion, at least 3 of the following 4 minor criteria must be present • In bone marrow biopsy or in section of other extracutaneous organs > 25% of mast cells are spindle shaped or have an atypical immature morphology† • Mast cells in bone marrow, peripheral blood or other extracutaneous organs express CD25, CD2, and/or CD30, in addition to mast cell markers • KIT D816V mutation or other activating KIT mutation detected in bone marrow, peripheral blood, or other extracutaneous organs*,‡ • Elevated serum tryptase level, persistently >20 ng/mL. In cases of SM-AMN an elevated tryptase does not count as a SM minor criterion. |
| Major criterion • Multifocal dense infiltrates of tryptase- and/or CD117 positive mast cells (≥15 mast cells in aggregates) detected in sections of bone marrow and/or other extracutaneous organ(s)* |
| In the absence of the major criterion, at least 3 of the following 4 minor criteria must be present • In bone marrow biopsy or in section of other extracutaneous organs > 25% of mast cells are spindle shaped or have an atypical immature morphology† • Mast cells in bone marrow, peripheral blood or other extracutaneous organs express CD25, CD2, and/or CD30, in addition to mast cell markers • KIT D816V mutation or other activating KIT mutation detected in bone marrow, peripheral blood, or other extracutaneous organs*,‡ • Elevated serum tryptase level, persistently >20 ng/mL. In cases of SM-AMN an elevated tryptase does not count as a SM minor criterion. |
In the absence of a KIT mutation particularly in cases with eosinophilia, the presence of tyrosine kinase gene fusions associated with M/LN-Eo must be excluded.
Round-cell well-differentiated morphology can occur in a small subset of cases. In these cases, the mast cells are often negative for CD25 and CD2 but positive for CD30.
To avoid “false-negative” results, use of a high sensitivity PCR assay for detection of KIT D816V mutation is recommended. If negative, exclusion of KIT mutation variants is strongly recommended in suspected SM.