Radiotherapy for Localized Prostate Cancer: Is Event-Free Survival Suitable Surrogate for Overall Survival?
Posted: Friday, September 11, 2020
Using a two-stage meta-analytic validation model, Christopher J. Sweeney, MBBS, of the Dana-Farber Cancer Institute, Boston, and colleagues found event-free survival, a composite endpoint based on prostate-specific antigen (PSA) level, cannot be considered a suitable surrogate for overall survival in men with localized prostate cancer treated with radiation therapy. The study was published in the Journal of Clinical Oncology.
Had event-free survival been shown to be an appropriate surrogate, it could have been “suitable for use as an intermediate clinical endpoint to substitute for overall survival to accelerate phase III (neo)adjuvant trials of prostate cancer therapies for primary radiation therapy–based trials,” wrote the team. Instead, event-free survival would be a weak surrogate, they explained, because at the patient level (stage 1 of the model), the correlation of event-free survival with overall survival was 0.43 (95% confidence interval [CI] = 0.42–0.44). At the trial level (stage 2 of the model), they continued, the R2 was 0.35 (95% CI = 0.01–0.60). “A clinically relevant surrogacy was defined a priori as an R2 ≥ 0.7,” wrote Dr. Sweeney and colleagues.
Nonetheless, they reported, further health economic analyses are underway to determine whether other metrics could be quantified to support the use of event-free survival as an endpoint to accelerate (neo)adjuvant prostate cancer trials. Success in this endeavor would benefit patients and society at large, pointed out the investigators.
For this work, the team analyzed individual PSA and disease data from 10,350 patients who participated in 15 radiation therapy–based trials that enrolled between 1987 and 2011 and had a median follow-up of 10 years. The information was extracted from the Intermediate Clinical Endpoints in Cancer of the Prostate database.
Disclosure: The study authors’ disclosure information can be found at ascopubs.org.