The use of progression-free survival and response rate as surrogates for overall survival were supported by significant correlations between the endpoints, in randomized trials of advanced soft tissue sarcoma.

However, 3-month progression-free survival (PFS) and 6-month PFS were not significantly correlated with overall survival (OS) and were not recommended as surrogates for OS, according to the researchers.

Significant correlations were observed between overall survival and PFS (correlation coefficient, 0.61) and overall survival and response rate (0.51). Correlations between 3-month PFS and 6-month PFS with overall survival (0.27 and 0.31, respectively) were not significant.

“In soft tissue sarcoma, trial design is particularly challenging, owing to the rarity and heterogeneity of this disease. Time-based endpoints including PFS, 3-month PFS, and 6-month PFS are gaining popularity as primary endpoints in phase III RCTs [randomized controlled trials], despite the fact that current data support their use only to screen for effective drugs in phase II trials,” wrote Dr. Alona Zer of Princess Margaret Cancer Centre and the University of Toronto and colleagues (J Clin Oncol. 2016 March 7. Doi: 10.1200/JCO.2016.66.4581).

“Data show that the assessment of outcomes as a single point in time … only rarely mirrors the hazards of the same endpoint. … As such, the odds ratio for 3-month PFS or 6-month PFS likely do not approximate the hazard ratio for PFS, making it difficult to justify the use of these endpoints in definitive phase III trials.”

PFS and overall survival have shown poor correlation in other cancer types, and evidence suggests that survival post progression may influence the association, with weaker correlations at longer survival post progression. The majority of soft tissue sarcoma reports had survival post progression of less than 12 months, likely explaining the high correlation between PFS and overall survival.

The investigators performed a systematic review of 52 randomized controlled trials, published from 1974 to 2014, that included 9,762 patients who received systemic therapy for advanced/metastatic soft tissue sarcoma.

Comprehensive toxicity assessment was included in just 20 studies (47%) and poorly reported in 6 studies (14%). Few studies included quality of life as a secondary endpoint. The authors noted that in the soft tissue sarcoma setting in which the purpose of systemic treatment may be palliation of symptoms, this is a concern.

Over the 4 decades represented by the systematic review, several trends appeared. Overall, a low proportion of studies included intent-to-treat analyses and clearly defined primary endpoints, but these characteristics improved over time. Endpoint selection has shifted away from response rate in favor of time-based events, including PFS, 3-month PFS, and 6-month PFS. Overall survival was the primary endpoint in just 4% of studies. Studies published in the last 2 decades were more likely to be supported by industry (5% vs. 35%).

Dr. Zer and coauthors reported having no relevant financial disclosures.