Activity of erlotinib when dosed below the maximum tolerated dose for <i>EGFR</i>‐mutant lung cancer: Implications for targeted therapy development

<jats:sec><jats:title>BACKGROUND</jats:title><jats:p>Erlotinib is a standard first‐line therapy for patients who have metastatic nonsmall cell lung cancer (NSCLC) with epidermal growth factor receptor (<jats:italic>EGFR</jats:italic>) mutations. The recommended dose of 150 mg daily is the maximum tolerated dose (MTD). Few clinical data are available regarding its efficacy at doses less than the MTD.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>An institutional database was queried for patients with advanced NSCLC who were positive for <jats:italic>EGFR</jats:italic> L858R mutations or exon 19 deletions and had received treatment with erlotinib. The treatment course, including the erlotinib dose at initiation of treatment, at 4 months into therapy, and at disease progression, was retrospectively studied. Progression‐free survival (PFS) was compared between patients who received the MTD (150 mg) and those who received reduced‐dose erlotinib (≤100 mg).</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>In total, 198 eligible patients were identified. Thirty‐one patients (16%) were initiated on reduced‐dose erlotinib; they were older (<jats:italic>P</jats:italic> = .001) and had lower performance status (<jats:italic>P</jats:italic> = .01) compared with those who were initiated on erlotinib at the MTD. The response rate to reduced‐dose erlotinib was 77%. The median PFS of patients initiated on reduced‐dose erlotinib was 9.6 months versus 11.4 months for those initiated at the MTD, a difference that was not statistically significant (hazard ratio, 0.81; 95% confidence interval, 0.54‐1.21; <jats:italic>P</jats:italic> = .30). There was a nonsignificant trend toward higher rates of progression within the central nervous system with reduced‐dose erlotinib.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>At doses below the MTD, erlotinib treatment results in a high response rate and a prolonged median PFS. Review of the literature indicates that 15 of 30 small‐molecule inhibitors that are approved or in late‐stage development for cancer therapy have recommended doses below the MTD. When the toxicities of MTD dosing are a concern, an investigation of small‐molecule inhibitors at doses below the MTD is warranted. <jats:bold><jats:italic>Cancer</jats:italic> 2016;122:3456–63</jats:bold>. © <jats:italic>2016 American Cancer Society</jats:italic>.</jats:p></jats:sec>