Benign nodal nevi frequently harbor the activating V600E BRAF mutation

Mutational activation of the BRAF oncogene is the most common genetic alteration in cutaneous melanoma. Potentially, BRAF mutation analysis of sentinel lymph node (SLN) biopsies could enhance the detection of micrometastases and improve the accuracy of nodal staging for patients with melanoma. Nodal nevi are small aggregates of benign nevus cells that are commonly encountered in the SLNs of patients with melanoma. The status of the BRAF gene in nodal nevi is not known, but this unresolved issue is of critical importance to any future detection strategies that use genetic alterations as biomarkers of metastatic spread. Twenty-six nodal nevi from 26 patients were evaluated for the thymine (T)-->adenine (A) missense mutation at nucleotide 1796 of the BRAF gene using the LigAmp assay, which can detect 1 mutant allele among 10,000 wild-type alleles. For each case, a matching volume of adjacent lymphoid tissue was used as a negative control. BRAF mutations were detected in 13 of the 26 nodal nevi, but in just 1 of the 26 adjacent controls (50% vs. 4%, P<0.0005, Fisher exact). Novel strategies that rely on detection of putative melanoma-specific markers for the diagnosis of micrometastatic melanoma in SLNs need to take into account the molecular genetic profile of the benign nodal nevus. Indeed, these nodal nevi, like melanoma, frequently harbor activating mutations of the BRAF oncogene underscoring the potentially confounding impact of these inclusions on melanoma detection.