Negative predictive value of biopsy margins of dysplastic nevi: A single-institution retrospective review

Background: Biopsies of dysplastic nevi processed by bread-loafing allow for limited margin assessment; however, reported biopsy margins often influence management. Objective: To evaluate the negative predictive value of biopsy margins of dysplastic nevi. Methods: A retrospective search of a single academic institution's pathology database was conducted to identify all biopsy specimens of dysplastic nevi between January 1, 2015, and December 31, 2017. Biopsy specimen margin assessments were compared with excision pathology reports to calculate negative predictive value and to assess the frequency of residual nevus on excision after positive biopsy margins. Results: A total of 1245 dysplastic nevi from 934 patients were identified. Clear biopsy margins had a negative predictive value for the absence of residual nevus on excision of 87.3% for dysplastic nevi of moderate atypia or greater. Residual nevus was identified on excision in 29.41% of cases of dysplastic nevi of moderate atypia or greater when initial biopsy margins were positive. Limitations: This was a retrospective, single-institution study. The calculations likely overestimate the true negative predictive value of biopsy margins because of processing of excision specimens by bread-loafing. Conclusions: This study provides additional evidence that reported biopsy margins are not representative of true margin status.