Patients with systemic mast cell (MC) disease, but not those with cutaneous
mastocytosis, are at a high risk (10-30%) to develop life-threatening myel
ogenous malignancies. In a significant proportion of cases. myeloid leukemi
as occur. Using conventional criteria, such leukemias resemble acute mlyelo
id leukemia (AML), chronic myeloid leukemia (CML), or myelomonocytic leukem
ia (CMML). Mast cell leukemia (MCL) may also occur. Myeloid leukemias (AML,
CML, CMML) can develop in indolent or aggressive mastocytosis (skin lesion
s present or absent) with a variable prephase of MG disease. By contrast, M
CL (typically without skin lesions) often develops on a "de novo" basis, an
d, 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 v
ariable metachromasia and chloroacetate esterase expression, whereas an MPO
-positive, tryptase-negative phenotype supports the diagnosis of a myeloid
non-MG lineage disease. Thus, MCL, but also myeloid non-MC lineage leukemia
s can develop in patients with (systemic) mastocytosis. Little is known, ho
wever, about the pathophysiologic basis of co-evolution. In the present art
icle, the concomitant occurrence of mastocytosis and leukemia is discussed
in the light of the literature and of concepts proposed to explain the biol
ogic basis of this phenomenon.