Although OS seems to be the most reliable outcome, other frequently used outcomes include tumor measurements and biomarkers. PFS or DFS may be considered to be of benefit to the patient, but they are often not validated as surrogate outcomes for OS. The validation of tumor measurements and biomarkers as surrogates for survival is difficult. For each indication separately, robust evaluations are needed to investigate whether a correlation exists between effects on survival and tumor measurements or biomarkers. For the sake of clarity, categories of endpoints as used in this manuscript are stated below.|
1. Overall survival (OS): Time from randomization until death from any cause.
2. Tumor measurements: Progression-free survival (PFS), disease-free survival (DFS) (=recurrence-free survival (RFS)), time to progression (TTP), time to treatment failure (TTF), objective response rate (ORR).
3. Symptom assessment: Time to progression of cancer symptoms, quality of life (QoL)
4. Biomarker: Characteristic that should be capable of objectively measuring and evaluating a normal biological process, a pathological process or the pharmacological response to a therapeutic intervention. Generally assayed from blood or body fluids. The validity of biomarkers as endpoints in trials remains to be established.