Evaluation of time to failure of strategy as an alternative surrogate endpoint in patients with lung cancer with EGFR mutations

Background Epidermal growth factor receptor (EGFR) is one of the most common oncogenes in non-small cell lung cancer (NSCLC). EGFR-tyrosine kinase inhibitor (TKI) and platinum-doublet chemotherapy (PT) are effective regimens in patients with NSCLC harbouring EGFR mutations. Among these patients, progression-free survival (PFS) has been used as a surrogate endpoint; however, it may not correlate with overall survival (OS) due to crossover. Time to failure of strategy (TFS) has been proposed as an alternative endpoint in advanced colorectal cancer clinical trials where multiple effective therapies are provided either in combination or sequentially. Nevertheless, it remains unclear whether TFS is useful in lung cancer trials. Patients and methods We retrospectively reviewed patients with NSCLC harbouring EGFR mutations who chose a treatment strategy consisting of EGFR-TKI and PT as the initial two regimens at the National Cancer Center Hospital. We evaluated the relationship between PFS and OS and between TFS and OS. Results Between May 2005 and April 2015, a total of 374 patients were diagnosed with NSCLC harbouring EGFR mutations. Among them, 158 patients were eligible for analysis. The median PFS, TFS and OS of the patients were 11.2 months (95% CI 9.9 to 12.6), 21.3 months (95%  CI 18.6 to 26.2) and 36.6 months (95%  CI 32.0 to 41.8), respectively. OS and TFS, but not PFS, were better in patients who received PT then EGFR-TKI compared with those who received the opposite schedule. The non-parametric Spearman’s rank correlation coefficients (r) between PFS and OS and between TFS and OS were 0.54 and 0.85, respectively. Conclusions This is the first report describing TFS data among patients with NSCLC with EGFR mutations who received EGFR-TKI and PT as the initial two regimens. TFS was acceptable as a surrogate endpoint for OS. Further validation in clinical trials is needed.