Prognostically relevant breakdown of 123 patients with systemic mastocytosis associated with other myeloid malignancies.

The prognostic heterogeneity of the World Health Organization category of "systemic mastocytosis with associated clonal hematologic nonmast cell lineage disease" (SM-AHNMD) has not been systematically validated by primary data. Among 138 consecutive cases with SM-AHNMD, 123 (89%) had associated myeloid neoplasm: 55 (45%) myeloproliferative neoplasm (SM-MPN), 36 (29%) chronic myelomonocytic leukemia, 28 (23%) myelodysplastic syndrome (SM-MDS), and 4 (3%) acute leukemia. Of the myeloid subgroups, SM-MPN displayed a 2- to 3-fold better life expectancy (P = .003), whereas leukemic transformation was more frequent in SM-MDS (29%; P = .02). The presence of eosinophilia, although prevalent (34%), was prognostically neutral, and the overall results were not affected by exclusion of FIP1L1-PDGFRA-positive cases. We conclude that it is clinically more useful to consider specific entities, such as SM-MPN, systemic mastocytosis with chronic myelomonocytic leukemia, SM-MDS, and systemic mastocytosis with-acute leukemia, rather than their broad reference as SM-AHNMD.