In [[clinical research]], particularly in oncology, **overall survival (OS)** is the length of time from either: - the date of diagnosis of a disease, or - the start of treatment **until death from any cause**. It is a **time-to-event endpoint** that measures how long patients live, regardless of whether death is related to the disease being studied or to something else. Because OS is objective (death is unambiguous), it is often considered the **gold standard endpoint** in cancer clinical trials when assessing treatment efficacy. 👉 Example: If a trial reports a median OS of 24 months, it means that 50% of patients were still alive 24 months after diagnosis or treatment initiation.