Efficacy of S-1 after pemetrexed in patients with non-small cell lung cancer: A retrospective multi-institutional analysis.

Background: S-1 and pemetrexed (PEM) are key treatments for non-small cell lung cancer (NSCLC). However, the mechanism of anticancer activity of S-1 and PEM is similar. Cross-resistance between S-1 and PEM is of concern. This exploratory study was designed to evaluate the treatment effect of S-1 following PEM-containing treatment.

Methods: This retrospective study included patients with advanced (c-stage III or IV, UICC seventh edition) or recurrent NSCLC who received S-1 monotherapy following the failure of previous PEM-containing chemotherapy at six hospitals in Japan. The primary endpoint of the study was the overall response rate (ORR). The secondary endpoint was the disease control rate (DCR), time to treatment failure (TTF), progression-free survival (PFS), and overall survival (OS).

Results: A total of 53 NSCLC patients met the criteria for inclusion in the study. Forty-six patients had adenocarcinoma (88.7%) and no patients had squamous cell carcinoma. Thirty-one patients (58.5%) received the standard S-1 regimen and 18 patients (34.0%) received the modified S-1 regimen. ORR was 1.9% (95% confidence interval [CI]: 0.00%-10.1%). Median TTF, PFS, and OS were 65, 84, and 385 days, respectively.

Conclusions: Although there were several limitations in this study, the ORR of S-1 after PEM in patients with nonsquamous (non-SQ) NSCLC was low compared to the historical control. One of the options in the future might be to avoid S-1 treatment in PEM-treated patients who need tumor shrinkage.