Risk of skin cancer among patients with myotonic dystrophy type 1 based on primary care physician data from the U.K. Clinical Practice Research Datalink.

Myotonic dystrophy type 1 (DM1) is an inherited multisystem neuromuscular disorder caused by a CTG trinucleotide repeat expansion in the DMPK gene. Recent evidence documents that DM1 patients have an increased risk of certain cancers, but whether skin cancer risks are elevated is unclear. Using the U.K. Clinical Practice Research Datalink (CPRD), we identified 1,061 DM1 patients and 15,119 DM1-free individuals matched on gender, birth year (±2 years), attending practice and registration year (±1 year). We calculated the hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of DM1 diagnosis with skin cancer risk using Cox proportional hazards models, for all skin cancers combined and by histological subtype. Follow-up started at the latest of the age at practice registration, DM1 diagnosis/control selection or January 1st 1988, and ended at the earliest of the age at first skin cancer diagnosis, death, transfer out of the practice, last date of data collection or the end of the CPRD record (October 31, 2016). During a median follow-up of 3.6 years, 35 DM1 patients and 108 matched DM1-free individuals developed a skin cancer. DM1 patients had an increased risk of skin cancer overall (HR = 5.44, 95% CI = 3.33-8.89, p < 0.0001), and basal cell carcinoma (BCC) (HR = 5.78, 95% CI = 3.36-9.92, p < 0.0001). Risks did not differ by gender, or age at DM1 diagnosis (p-heterogeneity > 0.5). Our data confirm suggested associations between DM1 and skin neoplasms with the highest risk seen for BCC. Patients are advised to minimize ultraviolet light exposure and seek medical advice for suspicious lesions.