September 2011 ASCO 2011 Bloom KJ
Early clinical trials have shown that vemurafenib has dramatic activity in patients with BRAF V600 mutation- positive metastatic melanoma.1,2 Preclinical and phase I clinical data show the drug has minimal activity in tumours lacking BRAF mutations, which creates the need for an accurate diagnostic test to identify appropriate patients for therapy.
At ASCO 2011, Bloom and colleagues presented on molecular testing for BRAF V600 mutations in the BRIM-2 trial, a phase II trial of vemurafenib in patients with BRAF V600 mutation-positive metastatic melanoma.3
- To assess eligibility for BRIM-2, tumour samples were screened with an investigational PCR assay (cobas 4800 BRAF V600 Mutation Test) designed to detect the canonical V600E (1799T > A) mutation.
- 328 samples were tested, of which 327 samples gave valid results.
- BRAF mutations were detected in 184 samples (56.3%).
- 132 with BRAF-mutation positive melanoma were enrolled in the trial based on clinical eligibility criteria.
- Sanger sequencing was performed retrospectively on DNA samples from all enrolled patients.
- 15 samples (11.4%) gave invalid Sanger results.
- Sanger methods detected a V600E mutation in 97 samples (73.5%), V600K mutation in nine samples (6.8%), and a wild-type result in 11 cases (8.3%). (Table 1)
- Samples were also subjected to deep sequencing with a quantitative picotiter plate pyrosequencing method to resolve differences between PCR and Sanger results.
- Using 454 sequencing of samples with invalid Sanger results revealed a V600E mutation in 14 cases, and a V600K mutation in one case.
- Of 11 samples with a wild type Sanger result, 454 sequencing detected a V600E mutation in all cases, with a median percentage of mutant alleles of 8%; 10 of the 11 samples had a percentage <25%.
- The presence of a V600K mutation was confirmed by 454 sequencing in all nine samples identified as having V600K mutations by Sanger.
- Molecular testing for BRAF V600 mutations in the BRIM-2 trial showed that the investigational PCR test had a low failure rate.
- The PCR test was more sensitive in the detection of V600E mutations than Sanger sequencing, which may miss mutations in cases with a low percentage of mutant alleles.
- The PCR test detects V600K mutations.
- In all 132 cases, a codon 600 mutation was confirmed by Sanger and/or 454 sequencing.
- This multicentre clinical trial achieved robust, rapid and accurate molecular testing.
References: 1. Flaherty KT, Puzanov I, Kim KB, et al. Inhibition of mutated, activated BRAF in metastatic melanoma. N Engl J Med 2010;363:809–819. 2. Ribas A, Kim KB, Schuchter LM, et al. BRIM-2: An open-label, multicenter phase II study of RG7204 (PLX4032) in previously treated patients with BRAF V600E mutation-positive metastatic melanoma. J Clin Oncol (ASCO Annual Meeting Abstracts) 2011;29:8509. 3. Bloom KJ, Anderson SM, Schilling RC, et al. Molecular testing for BRAF V600 mutations in the BRIM-2 trial of the BRAF inhibitor RG7204 (PLX4032) in metastatic melanoma. J Clin Oncol (ASCO Annual Meeting Abstracts) 2011;29:10523.