Supplementary Material for: Incidence of tattoo-associated melanoma in the Netherlands (1991-2023): a nationwide registry study

Background: Tattooing is an increasingly prevalent practice that is associated with various clinical complications. The carcinogenic potential of tattoo pigments remains unclear. While 45 case reports have described melanomas colocalizing with tattoos thus far, a pathogenetic link between tattoos and melanomas remains unproven. No nationwide epidemiological study has investigated the incidence of tattoo-associated melanoma (TAM).

Objectives: To determine the incidence of TAM in the Netherlands from 1991 to 2023, analyse TAM characteristics and patient demographics, and compare these findings with melanoma data from the general Dutch population during the same period.

Methods: Data were obtained from the nationwide network and registry of histo- and cytopathology in the Netherlands (PALGA). Malignant and benign melanocytic lesions on the tattooed skin were included. Patient demographics and melanoma characteristics were extracted and analysed. Data from the Netherlands Cancer Registry were used for comparison.

Results: From 1991 to 2023, 94 TAMs and 467 benign melanocytic lesions on tattoos were identified. The annual incidence of TAMs has increased over time. TAMs were diagnosed at an overall median age of 48.0 years, predominantly in males (64.9%). The median Breslow thickness was 0.9 mm, and most TAMs were TNM stage I (76.6%). The number-needed-to-excise was 6.0.

Discussion: 94 unique TAMs were identified in the Netherlands, which makes the largest case series to date. However, TAM incidence remained low (0.07%) compared to the total melanoma incidence, indicating that tattoos likely do not increase the risk of melanoma. A diagnostic delay from obscuring was considered unlikely based on the presented findings.

Conclusion: This nationwide cohort study found no evidence supporting a causal relationship between tattoos and melanoma.