What is Overall Survival (OS) in clinical trials?

Definition

Refers to the time from randomization (or initiation of treatment in single-arm trials) to death from any cause.

Positioning

Overall Survival (OS) is the only endpoint solely based on survival events, fairly objective, and precisely measurable. Therefore, it is recognized as the most reliable endpoint in randomized controlled clinical trials to measure the clinical benefits of anti-tumor drugs, known as the gold standard in clinical trials endpoints for anti-tumor drugs. The improvements in OS have statistical significance and clinical meaning, which can be used to support the routine application for the market approval of trial drugs.

Advantages

It is a widely accepted endpoint for clinical benefits, based on objectivity and quantification, and easy to measure and assess accurately.

Disadvantages

In clinical trials, the 5-year survival rate is often used, which usually requires a larger sample size and longer follow-up period. The study results could be affected by crossover phenomena and subsequent treatment. The inclusion of non-tumor deaths in the study outcomes also might influence the accuracy of the results. 

It's worth noting that comparing OS from different trials is not reliable. There can be heterogeneity among different trials in the areas of patient selection, standard care (SOC), and best supportive care (BSC). Therefore, it is recommended to use and interpret OS data with caution in single-arm trials.