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Background: In indolent systemic mastocytosis (ISM), several risk factors of disease progression have been identified. Previous studies, performed with limited patient numbers, have also shown that the clinical course in ISM is stable and comparable to that of cutaneous mastocytosis (CM). The aim of this project was to compare the prognosis of patients with ISM with that of patients with CM. Methods: We employed a dataset of 1993 patients from the registry of the European Competence Network on Mastocytosis (ECNM) to compare outcomes of ISM and CM. Results: We found that overall survival (OS) is worse in ISM compared to CM. Moreover, in patients with typical ISM, bone marrow mastocytosis (BMM), and smoldering SM (SSM), 4.1% of disease progressions have been observed (4.9% of progressions in typical ISM group, 1.7% in BMM, and 9.4% in SSM). Progressions to advanced SM were observed in 2.9% of these patients. In contrast, six patients with CM (1.7%) converted to ISM and no definitive progression to advanced SM was found. No significant differences in OS and event-free survival (EFS) were found when comparing ISM, BMM, and SSM. Higher risk of both progression and death was significantly associated with male gender, worse performance status, and organomegaly. Conclusion: Our data confirm the clinical impact of the WHO classification that separates ISM from CM and from other SM variants.

Background The WHO classification separates mastocytosis into distinct variants, but prognostication remains a clinical challenge. The aim of this study was to improve prognostication for patients with mastocytosis. Methods We analysed data of the registry of the European Competence Network on Mastocytosis including 1639 patients (age 17-90 years) diagnosed with mastocytosis according to WHO criteria between Jan 12, 1978, and March 16, 2017. Univariate and multivariate analyses with Cox regression were applied to identify prognostic variables predicting survival outcomes and to establish a prognostic score. We validated this International Prognostic Scoring System in Mastocytosis (IPSM) with data of 462 patients (age 17-79 years) from the Spanish network Red Espanola de Mastocitosis diagnosed between Jan 22, 1998, and Nov 2, 2017. Findings The prognostic value of the WHO classification was confirmed in our study (p<0.0001). For patients with non-advanced mastocytosis (n=1380), we identified age 60 years or older (HR 10.75, 95% CI 5.68-20.32) and a concentration of alkaline phosphatase 100 U/L or higher (2.91, 1.60-5.30) as additional independent prognostic variables for overall survival. The resulting scoring system divided patients with non-advanced mastocytosis into three groups: low (no risk factors), intermediate 1 (one risk factor), and intermediate 2 (two risk factors). Overall survival and progression-free survival differed significantly among these groups (p<0.0001). In patients with advanced mastocytosis (n=259), age 60 years or older (HR 2.14, 95% CI 1.42-3.22), a concentration of tryptase 125 ng/mL or higher (1.81, 1.20-2.75), a leukocyte count of 16 x 10(9) per L or higher (1.88, 1.27-2.79), haemoglobin of 11 g/dL or lower (1.71, 1.13-2.57), a platelet count of 100 x 10(9) per L or lower (1.63, 1.13-2.34), and skin involvement (0.46, 0.30-0.69) were prognostic variables. Based on these variables, a separate score for advanced mastocytosis with four

[Background]: The WHO classification separates mastocytosis into distinct variants, but prognostication remains a clinical challenge. The aim of this study was to improve prognostication for patients with mastocytosis., [Methods]: We analysed data of the registry of the European Competence Network on Mastocytosis including 1639 patients (age 17–90 years) diagnosed with mastocytosis according to WHO criteria between Jan 12, 1978, and March 16, 2017. Univariate and multivariate analyses with Cox regression were applied to identify prognostic variables predicting survival outcomes and to establish a prognostic score. We validated this International Prognostic Scoring System in Mastocytosis (IPSM) with data of 462 patients (age 17–79 years) from the Spanish network Red Española de Mastocitosis diagnosed between Jan 22, 1998, and Nov 2, 2017., [Findings]: The prognostic value of the WHO classification was confirmed in our study (p<0·0001). For patients with non-advanced mastocytosis (n=1380), we identified age 60 years or older (HR 10·75, 95% CI 5·68–20·32) and a concentration of alkaline phosphatase 100 U/L or higher (2·91, 1·60–5·30) as additional independent prognostic variables for overall survival. The resulting scoring system divided patients with non-advanced mastocytosis into three groups: low (no risk factors), intermediate 1 (one risk factor), and intermediate 2 (two risk factors). Overall survival and progression-free survival differed significantly among these groups (p<0·0001). In patients with advanced mastocytosis (n=259), age 60 years or older (HR 2·14, 95% CI 1·42–3·22), a concentration of tryptase 125 ng/mL or higher (1·81, 1·20–2·75), a leukocyte count of 16 × 109 per L or higher (1·88, 1·27–2·79), haemoglobin of 11 g/dL or lower (1·71, 1·13–2·57), a platelet count of 100 × 109 per L or lower (1·63, 1·13–2·34), and skin involvement (0·46, 0·30–0·69) were prognostic variables. Based on these variables, a separate score for advanced mastocytosis with four risk categories was established, with significantly different outcomes for overall survival and progression-free survival (p<0·0001). The prognostic value of both scores was confirmed in 413 patients with non-advanced disease and 49 with advanced mastocytosis from the validation cohort., [Interpretation]: The IPSM scores for patients with non-advanced and advanced mastocytosis can be used to predict survival outcomes and guide treatment decisions. However, the predictive value of the IPSM needs to be confirmed in forthcoming trials.