TOPLINE:

Patients with mastocytosis had more than double the risk for malignant melanoma (MM) and melanoma in situ (Mis) and a markedly higher risk for basal cell carcinoma (BCC) than matched healthy individuals. A large proportion of skin cancers were diagnosed around the time of their mastocytosis diagnosis, suggesting that detection bias may have influenced the findings.

METHODOLOGY:

• Researchers analysed records from the Swedish National Patient Register and Swedish Cancer Register to identify patients with primary or secondary mastocytosis between 2001 and 2018.
• A total of 2040 adult patients with mastocytosis (median age at diagnosis, 50.6 years; 59.4% women) were compared with 10,193 matched mastocytosis-free individuals.
• The analysis included the assessment of the risk for MM and Mis in patients with mastocytosis, including the timing of diagnoses before and after their mastocytosis diagnosis, and the evaluation of their risk for BCC.

TAKEAWAY:

• The risk for MM and Mis was more than twofold higher in patients with mastocytosis than in healthy individuals (odds ratio [OR], 2.39; 95% CI, 1.8-3.2), and the risk for BCC was also elevated (OR, 1.79; 95% CI, 1.49-2.14).
• Among 63 patients with MM or Mis, 33 had their detection before mastocytosis diagnosis — 15 were diagnosed within 12 months prior to the date of mastocytosis diagnosis (hazard ratio [HR], 3.08; P < .001) and 18 were diagnosed at 3 years before the date of mastocytosis diagnosis (HR, 3.08; P < .001) — and 30 were detected after the diagnosis (HR, 2.39; P < .001).
• Of 168 BCC records, 95 cases were detected after mastocytosis diagnosis (HR, 1.77; P < .001). The number of cases increased from 73 to 113 before diagnosis when including cases detected at 1 year before the date of mastocytosis diagnosis (HR, 1.91; P < .001).
• The majority of patients with mastocytosis presented with MM before the date of mastocytosis diagnosis (27 out of 39), and most presented with Mis after diagnosis (18 out of 24).

IN PRACTICE:

"We found an increased risk of MM/Mis and BCC in mastocytosis patients," the authors wrote, adding that "a substantial proportion of skin cancers were detected near the date of mastocytosis diagnosis, a finding likely to reflect at least in part an influence of detection bias."

SOURCE:

This study was led by Anna Bergström, Department of Medical Sciences, Dermatology and Venereology, Uppsala University, Akademiska University Hospital, Uppsala, Sweden. It was published online on August 18, 2025, in Acta Dermato-Venereologica.

LIMITATIONS:

This study lacked information on the World Health Organization classification of mastocytosis subtypes in the registers. The limited follow-up time may have led to an underestimation of mastocytosis-related skin tumour rates. Additionally, data on ultraviolet treatment history and sun exposure were not available.

DISCLOSURES:

This study was funded by the Swedish Cancer Society and Region Uppsala (ALF grant). The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.