Histological and immunohistochemical findings in recurrent nevi

Recurrent nevi (RN) arise from the incomplete removal of a benign melanocytic lesion. They may present with clinical and dermoscopic characteristics similar to melanomas and are a potential mimic of neoplasia.

To describe histopathological and immunohistochemical findings of recurrent nevi, including BRAF immunoexpression.

A cross-sectional study was conducted on 58 recurrent nevi obtained from a previous prospective study. RN were submitted to histopathological and immunohistochemical analysis. The markers HMB-45, Tyrosinase, Ki-67, and BRAF V-600E were used.

A trizonal pattern was observed in 84.5% of cases and is defined by the presence of junctional melanocytic proliferation, scar tissue, and residual dermal nests. Furthermore, architectural asymmetry (56.9%), lentiginous hyperplasia (75.9%), fibrosis (98.4%), lymphocytic infiltrate (96.5%), and melanophages (79.2%) were identified. Dropping off was observed in 1.7%, adnexal involvement in 22.3%, a pagetoid distribution in 30%, and cell atypia in 15%. HMB-45 and tyrosinase were expressed in a gradient and were identified in 98.3% and 91.4%, respectively. Ki-67 was positive in all cases, and the mean proliferative index was 2.83%. BRAF expression was positive in 72.4%.

Limited sample size, evaluation by a single dermatopathologist, targeted immunohistochemical profiling, and the lack of red counterstaining could be potential limitations of the study.

RN are characterized by architectural asymmetry and a trizonal pattern. Nuclear atypia and a pagetoid distribution may be observed. RN cells have a low proliferative index and are positive for HMB-45 and tyrosinase. BRAF expression occurs in most recurrences and is heterogeneous in RN melanocytes.