Abstract P4-08-19: Progression-free survival or time to progression in comparative clinical trials of metastatic breast cancer as a potential surrogate for overall survival: A systematic review of 49 trials focusing on breast cancer subtype

Abstract

Abstract Background: Overall survival (OS) is the established endpoint to evaluate the effects of drug treatment in comparative clinical trials of metastatic breast cancer. But assessing OS requires long follow-up periods and large sample size, which raise costs and create long delays in the drug approval process. Progression-free survival (PFS) or time to progression (TTP) is considered as a surrogate for OS and is often used as an alternative to OS. In some cancers the two endpoints are highly correlated, but in others they are not. Furthermore, the effect of breast cancer (BC) subtypes on the surrogacy of PFS/TTP for OS has not been completely defined. Method: A systematic literature review of randomized control trials was conducted to identify studies that reported both the hazard ratio (HR) of PFS/TTP and OS for BC subtypes {i.e. estrogen receptor (ER) positive, HER2 positive, and triple negative (TN)}. The correlation between the HR of PFS/TTP and OS was evaluated using weighted Spearman's rank correlation. Results: A total of 49 trials (34 phase III trials and 15 phase II trials) were selected for analysis. Among these trials, there were 8 comparison trials between one chemotherapy and another chemotherapy regimen, 18 comparison trials between chemotherapy and chemotherapy plus molecularly-targeted therapy, 9 comparison trials between one endocrine therapy and another endocrine therapy, and 5 comparison trials between endocrine therapy and endocrine therapy plus molecularly-targeted therapy. There were 17 trials reporting the HR of PFS/TTP and OS for ER positive, 16 trials for HER2 positive, and 9 trials for TN BC. Weighted Spearman's rank correlation revealed that coefficient between the HR of PFS/TTP and OS was 0.721(p<.0001) for all trials, 0.873(p< .0001) for ER positive, 0.642(p=0.0055) for HER2 positive, and 0.615(p=0.078)for TN BC. Conclusion: There was a strong correlation between the HR of PFS/TTP and OS for ER positive BC, and a weak correlation between the HR of PFS/TTP and OS for HER2 positive and TN BC. The validity of using PFS/TTP as an OS surrogate marker was shown for metastatic BC, especially for ER positive BC. Citation Format: Tsukioki T, Taira N, Sakamaki K, Suzuki Y, Kajiwara Y, Hatono M, Takahashi Y, Kawata K, Kochi M, Iwamoto T, Ikeda H, Shien T, Doihara H. Progression-free survival or time to progression in comparative clinical trials of metastatic breast cancer as a potential surrogate for overall survival: A systematic review of 49 trials focusing on breast cancer subtype [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-08-19.