Treatment responses of BRAF mutant melanoma to BRAF inhibitors are often limited by the development of resistance.,This case report describes the use of multiplatform molecular profiling in sequential surgical samples of a treatment-resistant tumour site subjected to ongoing treatment with dabrafenib in a patient with metastatic cutaneous BRAF mutant melanoma.,Next-generation sequencing showed the presence of the V600E, fibroblast growth factor receptor 2 (FGFR2), phosphatase and tensin homologue (PTEN) and p53 gene mutations.,With a continuous presence of the BRAF V600E, FGFR2 and PTEN mutations and appearances of new mutations in the PTEN gene at R137H and T321fs and p53 R273C genes during ongoing treatment, this case report indicates intratumoural clonal evolution as a resistance mechanism.,Two new mutations, the G542E exon 12 mutation variant of the FGFR2 gene and the R273C mutation variant of the p53 gene, are reported for the first time in BRAF mutant melanoma.
We used a combination of whole-genome sequencing and in vitro validation to show that mutations that activated at least two pro-growth/survival pathways mediated intrinsic resistance to BRAF inhibition in a melanoma patient.,These data demonstrate how in-depth analysis can reveal intrinsic resistance to standard of care, providing an opportunity for alternative therapeutic strategies for patients who are likely to fail first-line treat-575 ment.,BRAF is mutated in ∼42% of human melanomas (COSMIC. http://www.sanger.ac.uk/genetics/CGP/cosmic/) and pharmacological BRAF inhibitors such as vemurafenib and dabrafenib achieve dramatic responses in patients whose tumours harbour BRAFV600 mutations.,Objective responses occur in ∼50% of patients and disease stabilisation in a further ∼30%, but ∼20% of patients present primary or innate resistance and do not respond.,Here, we investigated the underlying cause of treatment failure in a patient with BRAF mutant melanoma who presented primary resistance.,We carried out whole-genome sequencing and single nucleotide polymorphism (SNP) array analysis of five metastatic tumours from the patient.,We validated mechanisms of resistance in a cell line derived from the patient's tumour.,We observed that the majority of the single-nucleotide variants identified were shared across all tumour sites, but also saw site-specific copy-number alterations in discrete cell populations at different sites.,We found that two ubiquitous mutations mediated resistance to BRAF inhibition in these tumours.,A mutation in GNAQ sustained mitogen-activated protein kinase (MAPK) signalling, whereas a mutation in PTEN activated the PI3 K/AKT pathway.,Inhibition of both pathways synergised to block the growth of the cells.,Our analyses show that the five metastases arose from a common progenitor and acquired additional alterations after disease dissemination.,We demonstrate that a distinct combination of mutations mediated primary resistance to BRAF inhibition in this patient.,These mutations were present in all five tumours and in a tumour sample taken before BRAF inhibitor treatment was administered.,Inhibition of both pathways was required to block tumour cell growth, suggesting that combined targeting of these pathways could have been a valid therapeutic approach for this patient.