Melanoma risk is increased in patients with mycosis fungoides compared with patients with psoriasis and the general population

Patients with mycosis fungoides (MF) are thought to be at increased risk of melanoma. However, studies addressing surveillance-bias and treatments as a possible confounder are lacking. This retrospective study compared the prevalence and risk of melanoma between 982 patients with MF, and 3,165 patients with psoriasis attending tertiary cutaneous-lymphoma/ psoriasis clinics during 2009 to 2018. Melanoma was diagnosed in 47 patients with MF (4.8%; 43 earlystage) and in 23 patients with psoriasis (0.7%) (odds ratio 6.6, p < 0.0001). In 60% of patients, MF/psoriasis preceded melanoma diagnosis. Hazard ratio (HR) for a subsequent melanoma in MF vs psoriasis was 6.3 (95% confidence interval (95% CI) 3.4–11.7, p < 0.0001). Compared with the general population, melanoma standardized incidence ratios were 17.5 in patients with MF (95% CI 11.0–23.9, p < 0.0001), and 2.2 (95% CI 0.6–3.8, p = 0.148) in patients with psoriasis. Narrow-band ultraviolet B was not a contributory factor (HR 1.15, 95% CI 0.62–2.14, p = 0.66). These findings add evidence that patients with MF have a significantly higher risk of melanoma, not only compared with the general population, but also compared with patients with psoriasis. This comorbidity may be inherent to MF.