eventfree

Event-free survival (EFS) is a metric used in clinical trials and oncology to describe the length of time after a starting point—such as diagnosis or initiation of treatment—during which a patient remains free from predefined adverse events. These events commonly include relapse or disease progression, the appearance of a new primary cancer, or death from any cause. The precise definition of the events can vary by study, and some trials include additional events such as treatment discontinuation due to toxicity. EFS is typically reported as a survival probability over time and is estimated using time-to-event analysis.

Calculation and interpretation: EFS is estimated with methods such as the Kaplan-Meier estimator, with censoring applied to patients who have not yet experienced an event by the end of follow-up. Hazard ratios may be derived from Cox proportional hazards models to compare treatments. Because the set of counted events can differ between studies, EFS is not directly comparable across trials without harmonized definitions. EFS is related to but distinct from progression-free survival (PFS), which is usually defined for advanced disease as time to progression or death; disease-free survival (DFS) refers to relapse-free survival after achieving remission.

Limitations and considerations: EFS can be influenced by differences in follow-up duration, assay sensitivity, and criteria for event adjudication. Censoring patterns and competing risks can affect estimates. When interpreting EFS, readers should consider the specific event definitions, patient population, and context of the trial.

See also: Survival analysis, Kaplan-Meier estimator, Cox proportional hazards model, progression-free survival, disease-free survival, overall survival.