Improved Classification of Melanocytic Nevi Using BRAF V600E Expression

Identifying histomorphologic features of a melanocytic neoplasm can provide relevant information on its molecular background, including the presence of the BRAF V600E mutation, which may help improve the accuracy of the classification and diagnosis of such tumors, according to the results of a retrospective histomorphologic and immunohistochemistry analysis published in the Journal of the American Academy of Dermatology.

The investigators retrospectively identified melanocytic nevi from their laboratory reporting system in the department of dermatology at the University of California, Davis, in Sacramento. They performed a histomorphologic analysis and BRAF V600E mutation expression analysis by immunohistochemistry.

A total of 150 histologically proven melanocytic nevi were included in the study.

BRAF V600E immunohistochemistry was performed in a total of 137 specimens. Of these, the staining was interpretable in 89 cases and of an indeterminate nature in 48 cases. Most of the cases deemed indeterminate were due to prominent melanin in melanocytes or keratinocytes (62.5%; 30 of 48) or to prominent melanin in melanocytes or keratinocytes, along with a small number of melanocytes (31.3%; 15 of 48). The remaining 3 cases were considered indeterminate because of weak staining (6.3%; 3 of 48).

Of the 89 interpretable cases, 14.8% (13 of 89) were wild-type (WT) and 86.4% (76 of 89) were positive for BRAF V600E by immunohistochemistry. Mean patient age was 53.5±11.3 in patients with BRAF WT and 48.0±16.7 in patients with BRAF V600E (P =.26).

Significant associations were revealed between the histomorphologic features of nevi and BRAF V600E expression. A predominantly junctional growth pattern was linked to BRAF WT nevi (84.6%; 11 of 13), whereas BRAF V600E nevi demonstrated a predominantly dermal growth pattern (55.3%; 42 of 76; P =.01). Most BRAF WT nevi did not exhibit congenital features (15.4%; 2 of 13) as opposed to BRAF V600E nevi (51.3%; 39 of 76; P =.02).

The investigators concluded that a greater understanding of the genotype-phenotype correlation in melanocytic nevi may enable the creation of a more accurate classification system for melanocytic tumors, which will ultimately lead to improved diagnostic accuracy and management of these common human tumors, along with enhanced understanding of markers and predictors of malignant transformation.

Reference

Kiuru M, Tartar DM, Qi L, et al. Improving classification of melanocytic nevi: BRAF V600E expression associated with distinct histomorphologic features [published online April 10, 2018]. J Am Acad Dermatol. pii: S0190-9622(18)30514-0. doi:10.1016/j.jaad.2018.03.052.