The bone marrow in systemic mastocytosis – an update

The bone marrow is the most common site of involvement in systemic mastocytosis (SM). The WHO has defined criteria for the diagnosis of SM and this review discusses the various patterns of bone marrow involvement by mast cell neoplasia and the roles of immunohistochemistry and flow cytometry in the diagnosis of SM. It also covers the morphologic features and diagnostic criteria for SM with associated clonal non-mast cell lineage haemopoietic neoplasms (SM-AHNMD) and aggressive mastocytosis (aleukaemic and leukaemic mast cell leukaemia, myelomastocytic overlap syndromes and mast cell sarcoma). In addition, this review covers unusual entities including reactive mast cell hyperplasia, well-differentiated systemic mastocytosis, chronic mast cell leukaemia and monoclonal mast cell activation syndrome.