Beyond Breslow Thickness: Reproducibility and Histopathologic Concordance of Ultra-High-Frequency Ultrasound in Primary Cutaneous Melanoma

Background: Ultra-high-frequency ultrasound (UHFUS) provides high-resolution assessment of superficial skin lesions, but evidence in melanoma has largely focused on preoperative thickness estimation. We evaluated the reproducibility of a structured UHFUS assessment and its histopathologic concordance in primary cutaneous melanoma. Methods: This single-center retrospective study included 320 treatment-naïve, histologically confirmed primary cutaneous melanomas examined with UHFUS (48–70 MHz) before excision. Two experienced radiologists independently assessed tumor thickness, horizontal diameter, surface discontinuity, deepest involved compartment, boundary definition, morphology, echostructure, and separate perilesional hypoechoic foci. Histopathology served as the reference standard. Reproducibility was assessed using ICC and κ statistics; UHFUS–Breslow agreement was evaluated using Lin’s concordance correlation coefficient (CCC) and Bland–Altman analysis. Results: Interobserver reproducibility was excellent for tumor thickness (ICC 0.96; 95% CI, 0.95–0.97) and horizontal diameter (ICC 0.94; 95% CI, 0.92–0.95). UHFUS thickness showed excellent concordance with Breslow thickness (CCC 0.95; 95% CI, 0.94–0.96 for both readers), with small positive biases (+0.12 and +0.10 mm). Exact agreement across predefined thickness strata was 90.0%. Surface discontinuity showed high sensitivity and specificity for histopathologic ulceration, whereas perilesional hypoechoic foci were highly specific but moderately sensitive for microsatellitosis. Increased tumor-infiltrating lymphocytes and an associated nevus component independently predicted greater UHFUS overestimation. Conclusions: Structured UHFUS provides reproducible quantitative and qualitative preoperative assessment of primary melanoma beyond thickness alone and may serve as a complementary imaging tool within specialized multidisciplinary pathways, while histopathology remains the reference standard for definitive diagnosis and staging.