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

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.