Table 5.
Global classification of MC disorders and pathologic MC reactions
| Proposed term | Primary definition |
|---|---|
| Mast cell hyperplasia1 | Increased numbers of nonclonal MCs, an underlying disease is usually found and no signs of |
| MCA are detectable; also seen in lymphoproliferative disorders and after administration of stem cell factor | |
| Mastocytosis (± MCAS) | Increased numbers of (mono)clonal MCs |
| Systemic mastocytosis | SM criteria (3 minor or 1 major + 1 minor) met (SM variants, including MCL) |
| Cutaneous mastocytosis | MIS criteria fulfilled but SM criteria not met (CM variants) |
| Mastocytoma | Localized, benign, presumably (mono)clonal |
| Mast cell sarcoma | Localized, aggressive (mono)clonal MCs |
| Mast cell activation syndrome | MCA by the criteria listed in table 2 |
| Primary MCAS | CM, SM or ‘(mono)clonal MCAS' |
| Secondary MCAS | Atopy or other disorder associated with MCA |
| Idiopathic MCAS | No reason for MCA found |
| Myelomastocytic conditions | MC lineage involvement in myeloid neoplasms |
| Tryptase+ AML | Criteria for SM or MML not met, tryptase+ blasts |
| Myelomastocytic leukemia2 (± MCAS) | MC lineage involvement in MDS/AML with at least 10% of all cells being clonal MCs in bone marrow or/and peripheral blood smears and no evidence/criteria for SM |
1
MC hyperplasia is not an intrinsic MC disorder, but is a reactive state that can be seen in a wide variety of conditions, and in many instances, the clinical significance and mechanisms of MC expansion remain unclear.
2
MML has not (yet) been included in the official WHO classification, although the condition is clearly defined by criteria, can clearly be discriminated from MCL and is of clinical significance because of the poor prognosis of these patients (similar to MCL but worse than other AML and MDS because of drug resistance). MIS = Mastocytosis in the skin; MDS = myelodysplastic syndrome.