Clinical significance of intronic variants in BRAF inhibitor resistant melanomas with altered BRAF transcript splicing.

Alternate BRAF splicing is the most common mechanism of acquired resistance to BRAF inhibitor treatment in melanoma. Recently, alternate BRAF exon 4-8 splicing was shown to involve an intronic mutation, located 51 nucleotides upstream of BRAF exon 9 within a predicted splicing branch point. This intronic mutation was identified in a single cell line but has not been examined in vivo. Herein we demonstrate that in three melanomas biopsied from patients with acquired resistance to BRAF inhibitors, alternate BRAF exon 4-8 splicing is not associated with this intronic branch point mutation. We also confirm that melanoma cells expressing BRAF splicing variants retain exquisite sensitivity to existing FDA-approved MEK inhibitors.