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

BackgroundIndolent systemic mastocytosis is a group of rare diseases for which reliable predictors of progression and outcome are still lacking.ObjectiveHere 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.MethodsA 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.ResultsMultivariate analysis showed that serum β2-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.ConclusionsIndolent 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 β2-microglobulin the most powerful independent parameters for predicting transformation into a more aggressive form of the disease.