AZD9291 in TKI EGFR resistance in non-small cell lung cancer and the new concept of phase I trials

Epidermal growth factor receptor (EGFR) tyrosine-kinase inhibitors (TKIs) constitute the standard of care for stage IV EGFR mutated non-small cell lung cancer (NSCLC) patients initiating firstline systemic treatment. Despite the initial remarkable activity of targeted treatment in these patients rendering objective response rates (ORR) of 50-80% and progression-free survivals (PFS) of 9-12 months, most patients present disease progression during the first 12 to 24 months. Although the activity of platinumbased doublets has been shown in EGFR mutated NSCLC patients after progression to first-line TKIs, PFS is rather short. Drug development companies have more recently focused their attention on the molecular basis of EGFR TKIs acquired resistance. Secondary resistance mutations have proven to be the most frequent cause of acquired resistance. Among them, T790M mutation in exon 20 seems to be the leading responsible for that resistance. Several agents have shown preliminary preclinical and clinical activity in overcoming acquired resistance to firstline EGFR TKIs. To date, however, only AZD9291, an oral, potent, irreversible EGFR TKI that is selective for EGFR tyrosine kinase inhibitor–sensitizing mutations and the T790M resistance mutation has shown to be not only highly active but also fairly tolerable in a large cohort of patients. Here we present a critical analysis of this trial in its clinical setting and propose some future directions.