Clinical and biologic diversity of leukemias occurring in patients with mastocytosis.

Patients with systemic mast cell (MC) disease, but not those with cutaneous mastocytosis, are at a high risk (10-30%) to develop life-threatening myelogenous malignancies. In a significant proportion of cases, myeloid leukemias occur. Using conventional criteria, such leukemias resemble acute myeloid leukemia (AML), chronic myeloid leukemia (CML), or myelomonocytic leukemia (CMML). Mast cell leukemia (MCL) may also occur. Myeloid leukemias (AML, CML, CMML) can develop in indolent or aggressive mastocytosis (skin lesions present or absent) with a variable prephase of MC disease. By contrast, MCL (typically without skin lesions) often develops on a "de novo" basis, and, if at all recognized, a prephase resembling (malignant) mastocytosis, is short. MCL differs from myeloid leukemias (AML, CML, CMML) by morphologic and phenotypic cellular characteristics. In fact, MCL are strongly tryptase-positive, c-kit-positive, myeloperoxidase (MPO) -negative neoplasms with variable metachromasia and chloroacetate esterase expression, whereas an MPO-positive, tryptase-negative phenotype supports the diagnosis of a myeloid non-MC lineage disease. Thus, MCL, but also myeloid non-MC lineage leukemias can develop in patients with (systemic) mastocytosis. Little is known, however, about the pathophysiologic basis of co-evolution. In the present article, the concomitant occurrence of mastocytosis and leukemia is discussed in the light of the literature and of concepts proposed to explain the biologic basis of this phenomenon.