Prognosis in adult indolent systemic mastocytosis: a long-term study of the Spanish Network on Mastocytosis in a series of 145 patients.

BACKGROUND: Indolent systemic mastocytosis is a group of rare diseases for which reliable predictors of progression and outcome are still lacking.

OBJECTIVE: Here we investigate the prognostic impact of the clinical, biological, phenotypic, histopathological, and molecular disease characteristics in adults with indolent systemic mastocytosis, who were followed using conservative therapy.

METHODS: A total of 145 consecutive patients were prospectively followed between January 1983 and July 2008; in addition, from 1967 to 1983, 20 patients were retrospectively studied.

RESULTS: Multivariate analysis showed that serum beta2-microglobulin (P = .003) together with the presence of mast/stem cell growth factor receptor gene (KIT) mutation in mast cells plus myeloid and lymphoid hematopoietic lineages (P = .02) was the best combination of independent parameters for predicting disease progression (cumulative probability of disease progression of 1.7% +/- 1.2% at 5-10 years and of 8.4% +/- 5.0% at 20-25 years). Regarding overall survival, the best predictive model included age >60 years (P = .005) and development of an associated clonal hematological non-mast cell disorder (P = .03) with a cumulative probability of death of 2.2% +/- 1.3% at 5 years and of 11% +/- 5.9% at 25 years.

CONCLUSIONS: Indolent systemic mastocytosis in adults has a low disease progression rate, and the great majority of patients have a normal life expectancy, with the presence of KIT mutation in all hematopoietic lineages and increased serum beta2-microglobulin the most powerful independent parameters for predicting transformation into a more aggressive form of the disease.