Regional Variations in Melanoma Histologic Characteristics: A Multicenter Cohort Study from Two Southeastern European Countries

Background/Objectives: Cutaneous melanoma prognosis is largely determined at diagnosis, with Breslow thickness, subtype and other histopathological aspects being key prognostic indicators. Variations in healthcare organization and environmental factors may influence melanoma presentation. This study aimed to compare epidemiological, clinical, and histopathological characteristics of primary cutaneous melanoma between two national referral centers in Southeastern Europe. Methods: A multicenter retrospective cohort study was conducted at the University Clinical Center of Serbia (Belgrade) and the Clinical Center of Montenegro (Podgorica). Consecutive patients treated for primary cutaneous melanoma between January 2018 and December 2022 were included. Data of interest were extracted from medical records. Annual regional sunshine hours were obtained from publicly available climatological databases. Group comparisons were performed using appropriate parametric and non-parametric tests, followed by a multivariable ordinal logistic regression analysis. Results: A total of 412 patients were analyzed. Age and sex distributions were comparable between cohorts. Nodular melanoma predominated in Montenegro, whereas superficial spreading melanoma was most common in Belgrade (p < 0.001). Median Breslow thickness was significantly higher in Montenegro (p = 0.001), with a greater proportion of tumors >4 mm (p = 0.001). In multivariable analysis, increasing age (p < 0.001), male sex (p = 0.027), and treatment in Montenegro (p = 0.001) were independently associated with higher Breslow thickness categories. Conclusions: Patients treated in Montenegro presented with thicker melanomas and a higher proportion of nodular subtype. These differences may reflect multifactorial influences, including healthcare accessibility and diagnostic pathways. Further prospective studies incorporating other histopathological aspects, time-to-diagnosis and survival outcomes are warranted.