Systemic Mastocytosis (SM)

The life expectancy of patients with systemic mastocytosis (SM), when regarded as a group, is shorter than that of the general population, with most deaths occurring within the first 3 to 5 years after diagnosis.1

In the updated 2016 World Health Organization (WHO) classification, SM is classified into 5 subtypes: indolent SM (ISM), smoldering SM (SSM), aggressive SM (ASM), SM with an associated hematological neoplasm (SM-AHN), and mast cell leukemia (MCL). Diagnosis using these subtypes impacts systemic mastocytosis life expectancy for patients.

A 2009 retrospective study of 342 adult patients with SM, conducted at Mayo Clinic between 1976 and 2007, aimed to estimate the life expectancy and mortality of SM patients within the context of the current WHO classification.2

In this study, the life expectancy of patients with ISM was found to be similar to that of the age- and sex-matched US population for the appropriate time period based on the date of diagnosis. The median overall survival (OS) for patients with ISM was 198 months, which was not significantly different from that of the healthy background population. In contrast, the median OS times of SM-AHN and ASM patients were 24 and 41 months, respectively. Patients with MCL were found to have the shortest median OS of only 2 months. Survival studies show that they were not significantly different from that of the control population.2

Indolent Systemic Mastocytosis

In a recent Danish population-based matched cohort study of patients with mastocytosis between 1977 and 2014, patients with ISM were found to have an increased risk of mortality compared to that of the general population. However, the authors suggested that this decreased survival may be attributed to the inclusion of SSM cases in the ISM category since SSM was not classified as an independent disease category until the 2016 WHO classification of SM. Patients with ISM are not classified as a new disease category. Hence, the authors recommended that survival estimates for patients with ISM be interpreted with caution as adult patients with CM, or SSM may be misclassified as ISM cases. Regrouping of patients with sensitivity analysis is recommended.3

In a study of 1993 patients from the registry of the European Competence Network on Mastocytosis (ECNM), the median OS of patients with ISM was found to be 28.4 years, and the 10-year OS was 93.5%.4,5

Another long-term study of 145 adult ISM patients conducted by the Spanish Network on Mastocytosis (REMA) found that patients with ISM had a long life expectancy and low rate of disease progression (3%), with increased serum β2-microglobulin levels and the presence of a KIT mutation (KITD816V) in all hematopoietic lineages as predictors of disease progression. D816V KIT mutation with the presence of serum b2-microglobulin in ISM is considered the best combination for predicting disease progression in the adult patient population.6

Life Expectancy for Smoldering Systemic Mastocytosis

In a 2018 study, the median OS of patients with SSM was found to be significantly lower than that of patients with ISM. This was explained by a higher prevalence of poor-risk features in SSM patients including older age, anemia, and thrombocytopenia.7

In a more recent study, the 10-year OS for individuals with SSM was 84.5%, and the median OS was not reached.5

Life Expectancy for Systemic Mastocytosis With an Associated Hematological Neoplasm

In the 2009 Mayo Clinic study, the median OS for patients with SM-AHN was 24 months, with leukemic transformation occurring in 13% of cases.2 

In the ECNM registry data, the median OS for patients with SM-AHN was 2.9 years. Further, the 10-year OS was 11.2% for individuals with SM-AHN.5

Life Expectancy for Aggressive Systemic Mastocytosis

In the Mayo Clinic study, the median OS in patients with ASM was 41 months, and leukemic transformation occurred in 5% of cases.2 

In the ECNM registry data, the median OS for patients with ASM was 5.7 years, and the 10-year OS was 44%.5

Life Expectancy for Mast Cell Leukemia

In the 2009 Mayo Clinic study, patients with MCL were found to have a very poor prognosis, with a very short median OS of only 2 months.2 In the ECNM registry data, the median OS for patients with MCL was 1.9 years, and the 10-year OS was 29.9%.5


  1. Pardanani A. Systemic mastocytosis in adults: 2021 update on diagnosis, risk stratification and management. Am J Hematol. 2021;96(4):508-525. doi:10.1002/ajh.26118
  2. Lim KH, Tefferi A, Lasho TL, et al. Systemic mastocytosis in 342 consecutive adults: survival studies and prognostic factors. Blood. 2009;113(23):5727-5736. doi:10.1182/blood-2009-02-205237
  3. Kibsgaard L, Deleuran M, Flohr C, Langan S, Braae Olesen A, Vestergaard C. How “benign” is cutaneous mastocytosis? A Danish registry-based matched cohort study. Int J Womens Dermatol. 2020;6(4):294-300. doi:10.1016/j.ijwd.2020.05.013
  4. Trizuljak J, Sperr WR, Nekvindová L, et al. Clinical features and survival of patients with indolent systemic mastocytosis defined by the updated WHO classification. Allergy. 2020;75(8):1927-1938. doi:10.1111/all.14248
  5. Sperr WR, Kundi M, Alvarez-Twose I, et al. International prognostic scoring system for mastocytosis (IPSM): a retrospective cohort study. Lancet Haematol. 2019;6(12):e638-e649. doi:10.1016/S2352-3026(19)30166-8
  6. Escribano L, Alvarez-Twose I, Sánchez-Muñoz L, et al. Prognosis in adult indolent systemic mastocytosis: a long-term study of the Spanish Network on Mastocytosis in a series of 145 patients. J Allergy Clin Immunol. 2009;124(3):514-521. doi:10.1016/j.jaci.2009.05.003
  7. Tefferi A, Shah S, Reichard KK, Hanson CA, Pardanani A. Smoldering mastocytosis: survival comparisons with indolent and aggressive mastocytosis. Am J Hematol. 2019;94(1):E1-E2. doi:10.1002/ajh.25302

Reviewed by Debjyoti Talukdar, MD, on 4/30/2022.