PURPOSE: Early administration of both epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) monotherapy and cytotoxic chemotherapy is crucial for non-small cell lung cancer (NSCLC) patients harboring EGFR mutations. We investigated the effect of first-line administration of these therapies on subsequent therapy in NSCLC patients. METHODS: This study enrolled 63 consecutive patients with advanced EGFR-mutant NSCLC and good performance status (PS) and who underwent first-line EGFR-TKI therapy or standard cytotoxic chemotherapy and then had progressive disease, from 2007 to 2011. The ability of each patient to receive the other therapy after first-line treatment failure was assessed. RESULTS: In the first-line setting, 23 and 40 patients received EGFR-TKI therapy and cytotoxic chemotherapy, respectively. At relapse, the EGFR-TKI therapy group showed more frequent PS deterioration (p = 0.042) and greater likelihood of symptomatic central nervous system (CNS) relapse (p = 0.093) compared with the cytotoxic chemotherapy group. Nine (39 %) of 23 patients initially receiving EGFR-TKI therapy could not receive standard cytotoxic therapy after progression mainly due to symptomatic CNS relapse. Only one (3 %) of 40 initially treated with cytotoxic chemotherapy failed to receive subsequent EGFR-TKI therapy (p < 0.001). Multivariate analysis revealed a correlation between the first-line therapy and the failure to switch to the other therapy after disease progression (OR 48.605, p = 0.005). CONCLUSION: In this study, patients who could not receive both EGFR-TKI therapy and cytotoxic chemotherapy in the early-line setting were included more in the first-line EGFR-TKI group, suggesting a potential risk associated with missing the timing of administration of subsequent therapy. Further investigation is warranted to detect their pretreatment clinical or molecular characteristics for development of a new treatment strategy specific for such subpopulation.