Lack of Response to Vemurafenib in Melanoma Carrying BRAF K601E Mutation

Vemurafenib has been developed to target common BRAF mutation V600E. It also exerts activity towards some but not all rare BRAF substitutions. Proper cataloguing of drug-sensitive and -insensitive rare mutations remains a challenge, due to low occurrence of these events and inability of commercial PCR-based diagnostic kits to detect the full spectrum of BRAF gene lesions. We considered the results of BRAF exon 15 testing in 1872 consecutive melanoma patients. BRAF mutation was identified in 1,090 (58.2%) cases. While drug-sensitive codon 600 substitutions constituted the majority of BRAF gene lesions (V600E: 962 [51.4%]; V600K: 86 [4.6%]; V600R: 17 [0.9%]), the fourth common BRAF allele was K601E accounting for 9 (0.5%) melanoma cases. The data on BRAF inhibitor sensitivity of tumors with K601E substitution are scarce. We administered single-agent vemurafenib to a melanoma patient carrying BRAF K601E mutation as the first-line treatment. Unfortunately, this therapy did not result in a tumor response. Taken together with already published data, this report indicates lack of benefit from conventional BRAF inhibitors in patients with BRAF K601E mutated melanoma.