Frequency of and factors associated with positive or equivocal margins in conventional excision of atypical intraepidermal melanocytic proliferations (AIMP): A single academic institution cross-sectional study

Background: No evidence-based surgical guidelines exist for atypical intraepidermal melanocytic proliferation (AIMP), a descriptive histopathologic diagnosis with uncertain malignant potential. Objective: We sought to identify the frequency of and risk factors associated with positive or equivocal margins after conventional excision. Methods: We conducted a retrospective cross-sectional study of 413 AIMPs treated by conventional excision. Results: Positive or equivocal margins were seen in 2.9% (12/413) of conventional excisions of AIMP. Risk factors associated with positive or equivocal margins included anatomic location on the head and neck (5/51, 9.8%; odds ratio 6.91, 95% confidence interval 1.93-24.80) (P =.012) and a preoperative biopsy specimen that included melanoma in situ in the differential diagnosis (11/214, 5.1%; odds ratio 10.73, 95% confidence interval 1.37-83.88) (P =.006). The frequency of positive or equivocal margins did not differ significantly with surgical margins greater than or less than 5 mm (odds ratio 0.61, 95% confidence interval 0.18-2.07) (P =.457). Limitations: This was a single-site, retrospective observational study. Conclusion: AIMP has a significantly increased risk for incomplete excision when it is located on the head and neck or has a preoperative histologic differential diagnosis that includes melanoma in situ. These subsets of AIMP may benefit from Mohs micrographic surgery or staged surgical excision to confirm clear margins before reconstruction.