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      Intrinsic Resistance to EGFR-Tyrosine Kinase Inhibitors in EGFR-Mutant Non-Small Cell Lung Cancer: Differences and Similarities with Acquired Resistance

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          Activating mutations in the epidermal growth factor receptor gene occur as early cancer-driving clonal events in a subset of patients with non-small cell lung cancer (NSCLC) and result in increased sensitivity to EGFR-tyrosine-kinase-inhibitors (EGFR-TKIs). Despite very frequent and often prolonged clinical response to EGFR-TKIs, virtually all advanced EGFR-mutated ( EGFRM+) NSCLCs inevitably acquire resistance mechanisms and progress at some point during treatment. Additionally, 20–30% of patients do not respond or respond for a very short time (<3 months) because of intrinsic resistance. While several mechanisms of acquired EGFR-TKI-resistance have been determined by analyzing tumor specimens obtained at disease progression, the factors causing intrinsic TKI-resistance are less understood. However, recent comprehensive molecular-pathological profiling of advanced EGFRM+ NSCLC at baseline has illustrated the co-existence of multiple genetic, phenotypic, and functional mechanisms that may contribute to tumor progression and cause intrinsic TKI-resistance. Several of these mechanisms have been further corroborated by preclinical experiments. Intrinsic resistance can be caused by mechanisms inherent in EGFR or by EGFR-independent processes, including genetic, phenotypic or functional tumor changes. This comprehensive review describes the identified mechanisms connected with intrinsic EGFR-TKI-resistance and differences and similarities with acquired resistance and among clinically implemented EGFR-TKIs of different generations. Additionally, the review highlights the need for extensive pre-treatment molecular profiling of advanced NSCLC for identifying inherently TKI-resistant cases and designing potential combinatorial targeted strategies to treat them.

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          Acquired resistance to TKIs in solid tumours: learning from lung cancer.

          The use of advanced molecular profiling to direct the use of targeted therapy, such as tyrosine kinase inhibitors (TKIs) for patients with advanced-stage non-small-cell lung cancer (NSCLC), has revolutionized the treatment of this disease. However, acquired resistance, defined as progression after initial benefit, to targeted therapies inevitably occurs. This Review explores breakthroughs in the understanding and treatment of acquired resistance in NSCLC, focusing on EGFR mutant and ALK rearrangement-positive disease, which may be relevant across multiple different solid malignancies with oncogene-addicted subtypes. Mechanisms of acquired resistance may be pharmacological (that is, failure of delivery of the drug to its target) or biological, resulting from evolutionary selection on molecularly diverse tumours. A number of clinical approaches can maintain control of the disease in the acquired resistance setting, including the use of radiation to treat isolated areas of progression and adding or switching to cytotoxic chemotherapy. Furthermore, novel approaches that have already proven successful include the development of second-generation and third-generation inhibitors and the combination of some of these inhibitors with antibodies directed against the same target. With our increased understanding of the spectrum of acquired resistance, major changes in how we conduct clinical research in this setting are now underway.
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            Clinical definition of acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors in non-small-cell lung cancer.

            Ten percent of North American patients with non-small-cell lung cancer have tumors with somatic mutations in the gene for the epidermal growth factor receptor (EGFR). Approximately 70% of patients whose lung cancers harbor somatic mutations in exons encoding the tyrosine kinase domain of EGFR experience significant tumor regressions when treated with the EGFR tyrosine kinase inhibitors (TKIs) gefitinib or erlotinib. However, the overwhelming majority of these patients inevitably acquire resistance to either drug. Currently, the clinical definition of such secondary or acquired resistance is not clear. We propose the following criteria be used to define more precisely acquired resistance to EGFR TKIs. All patients should have the following criteria: previous treatment with a single-agent EGFR TKI (eg, gefitinib or erlotinib); either or both of the following: a tumor that harbors an EGFR mutation known to be associated with drug sensitivity or objective clinical benefit from treatment with an EGFR TKI; systemic progression of disease (Response Evaluation Criteria in Solid Tumors [RECIST] or WHO) while on continuous treatment with gefitinib or erlotinib within the last 30 days; and no intervening systemic therapy between cessation of gefitinib or erlotinib and initiation of new therapy. The relatively simple definition proposed here will lead to a more uniform approach to investigating the problem of acquired resistance to EGFR TKIs in this unique patient population. These guidelines should minimize reporting of false-positive and false-negative activity in these clinical trials and would facilitate the identification of agents that truly overcome acquired resistance to gefitinib and erlotinib.
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              Rociletinib in EGFR-mutated non-small-cell lung cancer.

              Non-small-cell lung cancer (NSCLC) with a mutation in the gene encoding epidermal growth factor receptor (EGFR) is sensitive to approved EGFR inhibitors, but resistance develops, mediated by the T790M EGFR mutation in most cases. Rociletinib (CO-1686) is an EGFR inhibitor active in preclinical models of EGFR-mutated NSCLC with or without T790M. In this phase 1-2 study, we administered rociletinib to patients with EGFR-mutated NSCLC who had disease progression during previous treatment with an existing EGFR inhibitor. In the expansion (phase 2) part of the study, patients with T790M-positive disease received rociletinib at a dose of 500 mg twice daily, 625 mg twice daily, or 750 mg twice daily. Key objectives were assessment of safety, side-effect profile, pharmacokinetics, and preliminary antitumor activity of rociletinib. Tumor biopsies to identify T790M were performed during screening. Treatment was administered in continuous 21-day cycles. A total of 130 patients were enrolled. The first 57 patients to be enrolled received the free-base form of rociletinib (150 mg once daily to 900 mg twice daily). The remaining patients received the hydrogen bromide salt (HBr) form (500 mg twice daily to 1000 mg twice daily). A maximum tolerated dose (the highest dose associated with a rate of dose-limiting toxic effects of less than 33%) was not identified. The only common dose-limiting adverse event was hyperglycemia. In an efficacy analysis that included patients who received free-base rociletinib at a dose of 900 mg twice daily or the HBr form at any dose, the objective response rate among the 46 patients with T790M-positive disease who could be evaluated was 59% (95% confidence interval [CI], 45 to 73), and the rate among the 17 patients with T790M-negative disease who could be evaluated was 29% (95% CI, 8 to 51). Rociletinib was active in patients with EGFR-mutated NSCLC associated with the T790M resistance mutation. (Funded by Clovis Oncology; number, NCT01526928.).

                Author and article information

                Cancers (Basel)
                Cancers (Basel)
                01 July 2019
                July 2019
                : 11
                : 7
                [1 ]Department of Pathology, Rigshospitalet, Copenhagen University Hospital, DK-2100 Copenhagen, Denmark
                [2 ]Department of Oncology, Rigshospitalet, Copenhagen University Hospital, DK-2100 Copenhagen, Denmark
                [3 ]Department of Oncology and Palliative Units, Zealand University Hospital, DK-4700 Næstved, Denmark
                [4 ]Department of Clinical Genetics and Pathology, Skåne University Hospital, SE-221 85 Lund, Sweden
                Author notes
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (



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