Acquired resistance to targeted therapies in advanced non-small cell lung cancer: new strategies and new agents

Although the transition to molecularly defined patient subgroups in advanced non-small cell lung cancer (NSCLC) often leads to dramatic and prolonged responses to an inhibitor of an identified oncogenic mutation, acquired resistance eventually ensues. The optimal approach to management in that setting remains the subject of ongoing research, although it is possible to identify several points that distinguish it from traditional tenets based on conventional chemotherapy. Such patients are not equivalent to those who have progressed on first-line chemotherapy, and consideration of initiation of chemotherapy-based regimens as if the patient were being treated first line in the absence of an oncogenic mutation is a reasonable consideration. Acquired resistance is often partial; therefore, continued treatment with the same targeted therapy or another agent against the same target is a strategy favored by many experts, in part to minimize the risk of "rebound progression" that may occur when the targeted therapy is withdrawn. Progression within the central nervous system (CNS) may occur because of poor penetration of the systemic targeted therapy into the CNS, rather than true cellular resistance to the therapy itself; accordingly, local therapy for "brain only" progression with sustained targeted therapy for extracranial disease can be associated with prolonged disease control. Finally, patients with acquired resistance to a targeted therapy are ideal candidates for clinical trials when available, particularly when repeat biopsies of progressing lesions can help elucidate mechanisms of resistance and thereby lead to histologically and molecularly informed treatment decisions.

New strategies in overcoming acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors in lung cancer

The management of non-small cell lung carcinoma (NSCLC) has been transformed by the observation that lung adenocarcinomas harboring mutations in epidermal growth factor receptor (EGFR) are uniquely sensitive to EGFR tyrosine kinase inhibitors (TKI). In these patients, acquired resistance to EGFR-TKI develops after a median of 10 to 14 months, at which time the current standard practice is to switch to conventional cytotoxic chemotherapy. Several possible mechanisms for acquired resistance have been identified, the most common being the development of an EGFR T790M gatekeeper mutation in more than 50% of cases. In this review, we discuss recent advances in the understanding of acquired TKI resistance in EGFR-mutant lung cancer and review therapeutic progress with second generation TKIs and combinations of targeted therapies.