Anna Bergström: Mastocytosis: Registry-based studies of a rare condition

Abstract

Mastocytosis is a condition characterized by the accumulation of aberrant clonal mast cells in different organs and mediator related symptoms. It is divided into two major categories, cutaneous mastocytosis and systemic mastocytosis, with subtypes ranging from indolent to aggressive forms. Although mastocytosis is considered an uncommon condition, its epidemiology has for a long time been incompletely understood, as have several aspects of comorbidity in mastocytosis patients.

Paper I aimed to investigate the epidemiology of mastocytosis by estimating the incidence, prevalence and overall survival, and the comorbidity burden between individuals with mastocytosis and comparators using data from Swedish national registers. This population-based study found an annual incidence of 1.56 per 100,000 and a prevalence of 23.9 per 100,000, exceeding previous estimates from other studies. The comorbidity burden was higher in the mastocytosis patients, compared to comparators. We confirmed that the prognosis generally is favorable, but with marked survival differences between subtypes.

Paper II aimed to examine whether mastocytosis patients are at an increased risk of developing malignant melanoma (MM), melanoma in situ (MIS) or basal cell carcinoma (BCC) compared to the background population. By merging data from several Swedish population-based registries we found that patients with mastocytosis were at a more than two-fold higher risk for MM and MIS. The risk estimates for BCC were also elevated. We also found that a substantial portion of skin cancers were diagnosed near index date, suggesting a possible influence of detection bias.

Paper III further evaluated the risk of skin cancer through a large-scale, retrospective, propensity-score-matched cohort study utilizing data in a large U.S. healthcare database. We found that mastocytosis patients had significantly elevated lifetime risks of all skin cancers compared to comparators. Sensitivity analyses designed to assess detection bias indicated that detection bias alone cannot fully explain the increased risk of skin cancers in mastocytosis patients.

In conclusion, we found higher incidence and prevalence of mastocytosis than previously reported, along with evidence of a higher comorbidity burden. Additionally, our data suggest that patients with mastocytosis are at an increased risk of being diagnosed with skin cancer, warranting heightened dermatological surveillance.