Progression-free survival as a surrogate endpoint for overall survival in patients with third-line or later-line chemotherapy for advanced gastric cancer

Background: The correlation between overall survival (OS) and progression-free survival (PFS) has been evaluated in patients with metastatic or advanced gastric cancer who have received first-line and/or second-line chemotherapy. However, no corresponding analysis has been done for patients who have undergone third-line or later-line chemotherapy. Methods: A total of 303 patients from the Phase II/III studies of apatinib were pooled (the Phase II study as a training data set, the Phase III study as a testing data set). Landmark analyses of PFS at 2 months from randomization were performed to minimize lead time bias. The Cox proportional hazard model was used to test for the significance effect of PFS rate at 2 months in predicting OS. Additionally, the PFS/OS correlations were evaluated by the normal induced copula (National Institute for Health and Care Excellence) estimation model. Results: The median OS was 3.37 months (95% confidence interval 2.63-3.80) in patients who experienced progression at 2 months and 5.67 months in patients who did not (95% confidence interval 4.83-6.67; P<0.0001). Compared with patients who did not progress at 2 months, the adjusted hazard ratio for death was 3.39 (95% confidence interval 1.79-6.41; P<0.0001) for patients who experienced progression at 2 months. Moreover, the correlation of PFS/OS was 0.84 (95% confidence interval 0.74-0.90). Similar results were found in the testing data set. Conclusion: These results indicate that PFS correlates strongly with OS, suggesting PFS may be a useful early endpoint for patients with advanced gastric cancer who have undergone third-line or later-line chemotherapy. These observations require prospective validation.