relative survival

The share of people with a cancer who survive it, measured against how long similar people without that cancer would have lived, so that deaths from other causes do not count against it.

Cancer survival is usually reported as relative survival rather than as a plain headcount of who is still alive. The US National Cancer Institute's SEER programme defines it as an estimate of the percentage of patients who would be expected to survive the effects of their cancer, and says plainly that it excludes the risk of dying from other causes.

It works by comparison. Observed survival is the actual share of patients still alive at a given point after diagnosis, counting deaths from any cause at all. Relative survival sets that against the survival of people in the general population of the same age, race and sex who have not been diagnosed with cancer. An older group will lose some of its members to a heart attack or a stroke whatever their cancer does, and the comparison strips those losses out.

Five-year relative survival, the figure most often quoted, is the share expected to survive the effects of their cancer five years or more after diagnosis. It is a backward-looking measure: it describes people diagnosed years ago and treated with what was available then, so it can understate what someone diagnosed today should expect, particularly where treatment has changed recently.

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