Anatomical site and histological subtype as determinants of Breslow thickness and high-risk features in surgically managed cutaneous melanoma at Charlotte Maxeke Johannesburg Academic Hospital, Johannesburg, South Africa.

BACKGROUND: Breslow thickness is central to staging and prognosis in cutaneous melanoma and informs decisions on excision and nodal staging. We evaluated whether anatomical site and histological subtype predict Breslow thickness and selected high-risk pathological features in a surgically managed South African cohort, and whether Breslow thickness was associated with ulceration, mitotic rate, and nodal positivity. METHODS: We performed a retrospective observational study of surgically managed primary cutaneous melanoma at Charlotte Maxeke Johannesburg Academic Hospital, Johannesburg, South Africa, from January 2016 to December 2023. Breslow thickness was right-skewed and was summarised using medians with interquartile ranges. Categorical variables were summarised using counts and percentages. Adjusted associations with Breslow thickness were examined using multivariable linear regression on log-transformed Breslow thickness. Adjusted associations with ulceration and nodal positivity were examined using multivariable logistic regression. RESULTS: Ninety six melanomas were included. Breslow thickness was recorded in 88 cases, of which 86 had positive Breslow values for Breslow-based analyses. In the adjusted anatomical site model (n = 85), acral melanomas were thicker than trunk melanomas [ratio 2.32, 95% confidence interval (CI) 1.17-4.58, p = 0.016], and lower limb melanomas were also thicker than trunk melanomas (ratio 1.83, 95% CI 1.08-3.11, p = 0.025). In the adjusted subtype model (n = 72), acral lentiginous melanoma (ratio 3.49, 95% CI 1.86-6.56, p < 0.001) and nodular melanoma (ratio 2.92, 95% CI 1.60-5.35, p < 0.001) were thicker than superficial spreading melanoma. Lentigo maligna melanoma was also thicker than superficial spreading melanoma (ratio 3.52, 95% CI 1.93-6.40, p < 0.001), although this estimate was based on only five cases. Increasing Breslow thickness was associated with ulceration (odds ratio 2.90, 95% CI 1.67-5.04, p < 0.001), whereas neither Breslow thickness nor ulceration was independently associated with nodal positivity. CONCLUSION: Anatomical site and histological subtype identify recognisable groups at risk of presenting with thick melanoma. These findings support earlier biopsy and expedited surgical referral for acral, lower limb, and nodular appearing lesions in public sector pathways. Larger prospective studies with follow up data are needed to determine whether these patterns translate into differences in oncological outcomes.