Progression-free survival/time to progression as a potential surrogate for overall survival in HR+, HER2– metastatic breast cancer

• Main Authors: Forsythe A, Chandiwana D, Barth J, Thabane M, Baeck J, Tremblay G
• Format: Article
• Language: English
• Published: Dove Medical Press 2018-05-01
• Series: Breast Cancer : Targets and Therapy
• Subjects: Breast cancer; overall survival; progression-free survival; time to progression; correlation analysis; surrogate endpoint
• Online Access: https://www.dovepress.com/progression-free-survivaltime-to-progression-as-a-potential-surrogate--peer-reviewed-article-BCTT

Anna Forsythe,1 David Chandiwana,2 Janina Barth,3 Marroon Thabane,4 Johan Baeck,2 Gabriel Tremblay1 1Purple Squirrel Economics, New York, NY, 2Novartis Pharmaceuticals Corporation, East Hanover, NJ, USA; 3Novartis Pharma GmbH, Nuremberg, Germany; 4Novartis Pharmaceuticals Incorporated, Dorval, QC, Canada Background: Several recent randomized controlled trials (RCTs) in hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) metastatic breast cancer (MBC) have demonstrated significant improvements in progression-free survival (PFS); however, few have reported improvement in overall survival (OS). The surrogacy of PFS or time to progression (TTP) for OS has not been formally investigated in HR+, HER2– MBC.Methods: A systematic literature review of RCTs in HR+, HER2– MBC was conducted to identify studies that reported both median PFS/TTP and OS. The correlation between PFS/TTP and OS was evaluated using Pearson’s product–moment correlation and Spearman’s rank correlation. Subgroup analyses were performed to explore possible reasons for heterogeneity. Errors-in-variables weighted least squares regression (LSR) was used to model incremental OS months as a function of incremental PFS/TTP months. An exploratory analysis investigated the impact of three covariates (chemotherapy vs hormonal/targeted therapy, PFS vs TTP, and first-line therapy vs second-line therapy or greater) on OS prediction. The lower 95% prediction band was used to determine the minimum incremental PFS/TTP months required to predict OS benefit (surrogate threshold effect [STE]).Results: Forty studies were identified. There was a statistically significant correlation between median PFS/TTP and OS (Pearson =0.741, P=0.000; Spearman =0.650, P=0.000). These results proved consistent for chemotherapy and hormonal/targeted therapy. Univariate LSR analysis yielded an R2 of 0.354 with 1 incremental PFS/TTP month corresponding to 1.13 incremental OS months. Controlling the type of treatment (chemotherapy vs hormonal/targeted therapy), line of therapy (first vs subsequent), and progression measure (PFS vs TTP) led to an improved R2 of 0.569 with 1 PFS/TTP month corresponding to 0.78 OS months. The STE for OS benefit was 5–6 months of incremental PFS/TTP.Conclusion: We demonstrated a significant association between PFS/TTP and OS, which may justify the use of PFS/TTP as a surrogate for OS benefit in HR+, HER2– MBC. Keywords: breast cancer, overall survival, progression-free survival, time to progression, correlation analysis, surrogate endpoint