Skin lesions suspicious for melanoma: New Zealand excision margin guidelines in practice

Abstract INTRODUCTION: New Zealand guidelines for cutaneous melanoma management recommend excision biopsy specimens of suspected lesions have a 2 mm horizontal margin, and a deep margin into upper subcutis. AIM: To assess guideline compliance of suspicious lesion biopsies taken in the community and in a hospital. METHODS: Patients admitted to Waikato Hospital, Hamilton, for diagnostic or treatment melanoma surgery during the year ending February 2016 were retrospectively identified, and their demographic and biopsy characteristics examined. RESULTS: In total, 140 patients had excision biopsies: 61.4% were performed outside the hospital. Biopsy data were available for 126 specimens. Mean horizontal margin was greater (P = 0.001) in hospital biopsies (4.8 mm, standard deviation (s.d.) 3.7 mm) than biopsies performed elsewhere (2.8 mm; s.d. 1.8 mm). Horizontal margins >2.0 mm occurred in 70.6% of specimens; 21.6% of ≤2.0 mm specimens had a tumour-positive margin. Subsequent wide local excision identified residual melanoma in 9.6% of specimens, which was not associated (P = 0.3) with primary horizontal margin ≤2.0 mm. Mean deep margin of hospital biopsies (6.5 mm; s.d. 2.7 mm) was greater (P < 0.001) than in other biopsies (4.1 mm; s.d. 2.7 mm). Horizontal margin >2.0 mm specimens had greater (P < 0.001) mean deep margin (5.9 mm; s.d. 2.7 mm) than specimens with horizontal margin ≤2.0 mm (mean deep margin 3.3 mm; s.d. 2.7 mm). Deep margin ≤2.0 mm (19.0%) was independently associated with the facility where biopsy was performed (P = 0.001) and horizontal margin (P < 0.001). DISCUSSION: The New Zealand biopsy deep margin recommendation does not lend itself to meaningful audit. Compliance with the horizontal margin recommendation was low, but of uncertain clinical significance.