GP32: Are positive biopsy margins in melanoma significant? – A cohort study of micro- versus macroscopic margin status and their impact on residual disease and survival

Introduction: The presence of positive biopsy margins in melanoma can provoke anxiety over potential disease progression from delays to surgical excision, but their impact on outcomes is unknown. This study aimed to compare the presence of residual melanoma in the surgical excision specimen and survival between patients with negative, microscopically positive, and macroscopically positive biopsy margins.

Methods: Patients with cutaneous melanoma who underwent surgical excision over a 13-year period were included. Biopsy characteristics, residual disease in the surgical specimen, and overall and recurrence-free survival were compared between patients with negative, microscopically positive (only scar visible), and macroscopically positive (visible remaining melanoma) biopsy margins.

Results: Of 855 patients, 44.7%, 31.9%, and 23.4% had neg ative, m icroscopically positive, and macroscopically positive margins, respectively. Incidence of residual invasive melanoma in the surgical specimen varied (P < 0.001), occurring in 9.4%, 15.0%, and 76.5% of patients, respectively. Predictors of residual disease included microscopically positive (P=0.026) and macroscopically positive biopsy margins (P < 0.001). Kaplan-Meier curves demonstrated comparable survival between those with negative and microscopically positive margins, but overall (P < 0.001) and recurrence-free survival (P < 0.001) were significantly worse in the macroscopically positive margin group. These patients had worse prognosis melanoma, 17.0% being >4mm in Breslow thickness, 33.0% being ulcerated, and 22.9% having positive sentinel lymph nodes.

Conclusion: Patients and physicians may be reassured in the presence of microscopically positive biopsy margins which are not associated with worse survival and often have no further residual disease upon surgery. Patients with macroscopic residual melanoma must be prioritized for surgery due to their poorer prognosis.