Resistance surveillance in a BRAF mutant melanoma patient on long-term BRAF-inhibitor treatment – ScienceOpen
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      Resistance surveillance in a BRAF mutant melanoma patient on long-term BRAF-inhibitor treatment

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          Abstract

          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.

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          Melanomas acquire resistance to B-RAF(V600E) inhibition by RTK or N-RAS upregulation.

          Activating B-RAF(V600E) (also known as BRAF) kinase mutations occur in ∼7% of human malignancies and ∼60% of melanomas. Early clinical experience with a novel class I RAF-selective inhibitor, PLX4032, demonstrated an unprecedented 80% anti-tumour response rate among patients with B-RAF(V600E)-positive melanomas, but acquired drug resistance frequently develops after initial responses. Hypotheses for mechanisms of acquired resistance to B-RAF inhibition include secondary mutations in B-RAF(V600E), MAPK reactivation, and activation of alternative survival pathways. Here we show that acquired resistance to PLX4032 develops by mutually exclusive PDGFRβ (also known as PDGFRB) upregulation or N-RAS (also known as NRAS) mutations but not through secondary mutations in B-RAF(V600E). We used PLX4032-resistant sub-lines artificially derived from B-RAF(V600E)-positive melanoma cell lines and validated key findings in PLX4032-resistant tumours and tumour-matched, short-term cultures from clinical trial patients. Induction of PDGFRβ RNA, protein and tyrosine phosphorylation emerged as a dominant feature of acquired PLX4032 resistance in a subset of melanoma sub-lines, patient-derived biopsies and short-term cultures. PDGFRβ-upregulated tumour cells have low activated RAS levels and, when treated with PLX4032, do not reactivate the MAPK pathway significantly. In another subset, high levels of activated N-RAS resulting from mutations lead to significant MAPK pathway reactivation upon PLX4032 treatment. Knockdown of PDGFRβ or N-RAS reduced growth of the respective PLX4032-resistant subsets. Overexpression of PDGFRβ or N-RAS(Q61K) conferred PLX4032 resistance to PLX4032-sensitive parental cell lines. Importantly, MAPK reactivation predicts MEK inhibitor sensitivity. Thus, melanomas escape B-RAF(V600E) targeting not through secondary B-RAF(V600E) mutations but via receptor tyrosine kinase (RTK)-mediated activation of alternative survival pathway(s) or activated RAS-mediated reactivation of the MAPK pathway, suggesting additional therapeutic strategies.
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            Combined BRAF and MEK inhibition in melanoma with BRAF V600 mutations.

            Resistance to therapy with BRAF kinase inhibitors is associated with reactivation of the mitogen-activated protein kinase (MAPK) pathway. To address this problem, we conducted a phase 1 and 2 trial of combined treatment with dabrafenib, a selective BRAF inhibitor, and trametinib, a selective MAPK kinase (MEK) inhibitor. In this open-label study involving 247 patients with metastatic melanoma and BRAF V600 mutations, we evaluated the pharmacokinetic activity and safety of oral dabrafenib (75 or 150 mg twice daily) and trametinib (1, 1.5, or 2 mg daily) in 85 patients and then randomly assigned 162 patients to receive combination therapy with dabrafenib (150 mg) plus trametinib (1 or 2 mg) or dabrafenib monotherapy. The primary end points were the incidence of cutaneous squamous-cell carcinoma, survival free of melanoma progression, and response. Secondary end points were overall survival and pharmacokinetic activity. Dose-limiting toxic effects were infrequently observed in patients receiving combination therapy with 150 mg of dabrafenib and 2 mg of trametinib (combination 150/2). Cutaneous squamous-cell carcinoma was seen in 7% of patients receiving combination 150/2 and in 19% receiving monotherapy (P=0.09), whereas pyrexia was more common in the combination 150/2 group than in the monotherapy group (71% vs. 26%). Median progression-free survival in the combination 150/2 group was 9.4 months, as compared with 5.8 months in the monotherapy group (hazard ratio for progression or death, 0.39; 95% confidence interval, 0.25 to 0.62; P<0.001). The rate of complete or partial response with combination 150/2 therapy was 76%, as compared with 54% with monotherapy (P=0.03). Dabrafenib and trametinib were safely combined at full monotherapy doses. The rate of pyrexia was increased with combination therapy, whereas the rate of proliferative skin lesions was nonsignificantly reduced. Progression-free survival was significantly improved. (Funded by GlaxoSmithKline; ClinicalTrials.gov number, NCT01072175.).
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              Dabrafenib in BRAF-mutated metastatic melanoma: a multicentre, open-label, phase 3 randomised controlled trial.

              Dabrafenib, an inhibitor of mutated BRAF, has clinical activity with a manageable safety profile in studies of phase 1 and 2 in patients with BRAF(V600)-mutated metastatic melanoma. We studied the efficacy of dabrafenib in patients with BRAF(V600E)-mutated metastatic melanoma. We enrolled patients in this open-label phase 3 trial between Dec 23, 2010, and Sept 1, 2011. This report is based on a data cutoff date of Dec 19, 2011. Patients aged 18 years or older with previously untreated, stage IV or unresectable stage III BRAF(V600E) mutation-positive melanoma were randomly assigned (3:1) to receive dabrafenib (150 mg twice daily, orally) or dacarbazine (1000 mg/m(2) intravenously every 3 weeks). Patients were stratified according to American Joint Committee on Cancer stage (unresectable III+IVM1a+IVM1b vs IVM1c). The primary endpoint was investigator-assessed progression-free survival and was analysed by intention to treat; safety was assessed per protocol. This study is registered with ClinicalTrials.gov, number NCT01227889. Of the 733 patients screened, 250 were randomly assigned to receive either dabrafenib (187 patients) or dacarbazine (63 patients). Median progression-free survival was 5·1 months for dabrafenib and 2·7 months for dacarbazine, with a hazard ratio (HR) of 0·30 (95% CI 0·18-0·51; p<0·0001). At data cutoff, 107 (57%) patients in the dabrafenib group and 14 (22%) in the dacarbazine group remained on randomised treatment. Treatment-related adverse events (grade 2 or higher) occurred in 100 (53%) of the 187 patients who received dabrafenib and in 26 (44%) of the 59 patients who received dacarbazine. The most common adverse events with dabrafenib were skin-related toxic effects, fever, fatigue, arthralgia, and headache. The most common adverse events with dacarbazine were nausea, vomiting, neutropenia, fatigue, and asthenia. Grade 3-4 adverse events were uncommon in both groups. Dabrafenib significantly improved progression-free survival compared with dacarbazine. GlaxoSmithKline. Copyright © 2012 Elsevier Ltd. All rights reserved.
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                Author and article information

                Journal
                Melanoma Res
                Melanoma Res
                CMR
                Melanoma Research
                Lippincott Williams & Wilkins
                0960-8931
                1473-5636
                August 2014
                04 July 2014
                : 24
                : 4
                : 408-412
                Affiliations
                [a ]Medical Professorial Unit, Prince of Wales Hospital and University of New South Wales, Randwick, New South Wales, Australia
                [b ]Sarah Cannon Research UK and University College London, London, UK
                Author notes
                Correspondence to Gabriel Mak, MBBS, Medical Professorial Unit, Prince of Wales Hospital, University of New South Wales, Edmund Blackett Building, 1st Floor, South Wing, Randwick 2031, NSW, Australia Tel: +61 401 132 487; e-mails: gwhmak@ 123456gmail.com
                Article
                10.1097/CMR.0000000000000085
                4086757
                24858661
                67007463-fbdd-4124-8dc0-15e1175b0a0e
                © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins

                This is an open-access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0, where it is permissible to download, share and reproduce the work in any medium, provided it is properly cited. The work cannot be changed in any way or used commercially. http://creativecommons.org/licenses/by-nc-nd/3.0.

                History
                : 28 November 2013
                : 1 April 2014
                Categories
                Short Communications
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                metastatic melanoma,molecular profiling,treatment resistance

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