Evaluating Melanoma Risk in Adult Mastocytosis: Potential Impact of Detection Bias - A Registry-based Study (Sweden).

There is some evidence that mastocytosis patients are at increased risk of skin cancer. This study aimed to assess the risk of malignant melanoma (MM), melanoma in situ (Mis), and basal cell carcinoma (BCC). A dataset was generated by individual-level record linkages between Swedish population registers including the National Patient Register (NPR), the Swedish Cancer Register (SCR), and the Population Register (PR). Adult patients with a mastocytosis diagnosis between 2001 and 2018 were identified in the SCR and NPR. For each case, 5 mastocytosis-free comparators matched on age, sex, and county of residence were randomly chosen from the PR. Records of skin cancer were identified in the SCR and NPR. In total, the study encompassed 2,040 mastocytosis patients of whom 63 had a record of MM/Mis and 168 a record of BCC. Compared with comparators, the risk of MM/Mis was more than twofold higher (OR 2.39, 95% CI 1.8-3.2). Risk estimates for BCC were also elevated (OR 1.77, 95% CI 1.49-2.14). When assessing the timing of skin cancers, a substantial portion were diagnosed near index date. Taken together, in the present study these findings of increased risk of MM/Mis and BCC in mastocytosis patients may reflect an influence of detection bias.