Risk of malignant melanoma in hyperthyroid and hypothyroid female populations: Results from a large Danish cohort...

Experimental studies suggest that thyroid hormones may influence tumor development through endocrine and cellular signaling pathways. Although malignant melanoma (MM) is primarily associated with ultraviolet radiation exposure, the potential role of thyroid dysfunction in melanoma development remains unclear. We investigated the association between hyperthyroidism or hypothyroidism and the rate of MM in a nationwide cohort of Danish women.

Our cohort comprised 1,058,939 women born between January 1, 1960, and December 31, 1997, and was followed from 1996 to 2022. Information on thyroid disease, MM diagnoses, covariates and follow-up was obtained from Danish nationwide registries. Cox proportional hazards models with attained age as the underlying scale were used to estimate Hazard ratios (HRs) and 95% confidence intervals (CIs). Analyses were stratified by time since diagnosis, menopausal status and histological subtype.

Hyperthyroidism was not associated with the rate of overall MM (HR: 0.94; 95% CI: 0.79-1.12). For hypothyroidism, the HR for overall MM was 0.89 (95% CI: 0.77-1.02). Estimates for superficial spreading MM were similar. Among women diagnosed with hypothyroidism within the past 10 years, the HR for superficial spreading MM was 0.80 (95% CI: 0.66-0.98). Stratification by menopausal status did not materially alter the associations.

Our findings do not provide clear evidence of an association between thyroid dysfunction and the rate of MM in women. The observed decreased rate of superficial spreading MM among women with hypothyroidism within 10 years of diagnosis should be interpreted cautiously, as it was the only statistically significant finding among multiple subgroup analyses and may represent a chance finding. Further studies incorporating detailed clinical and biochemical measures of thyroid function are warranted.