Basics of Median Survival (MS)

Median survival is a statistic that refers to how long patients survive with a disease in general or after a certain treatment. It is the time — expressed in months or years — when half the patients are expected to be alive. It means that the chance of surviving beyond that time is 50 percent. It gives an approximate indication of survival as well as the prognosis of a group of patients with cancer. Median survival is a very commonly used term reported in all cancer treatment studies.

Examples

• “The estimated median survival was not reached for the low-risk group.” Here, the interpretation would be that, among the people in the study who had low-risk cancer, researchers could not calculate a median survival because more than half of them were still living.
• “Median survival times for intermediate- and high-risk groups were 10 and 5 years, respectively.” In this case, 50 percent of those with the intermediate-risk disease were still living 10 years after entering the study; for those with high-risk disease, half were still living 5 years after beginning the study.
• “Del(13q) is associated with a favorable prognosis and the longest median survival (133 months).” Del(13q) is a chromosomal abnormality found in chronic lymphocytic leukemia or CLL. Chromosomal abnormalities are the subject of the field of cytogenetics and they are detected using tests. In this example, they are saying that, in a particular group with a particular type of CLL, having the Del(13q) abnormality — as opposed to other abnormalities they tested for — was associated with the longest survival: half of those with this genetic abnormality in a certain study was still living 133 months later.

Similar or Related Terms

• Median survival time
• Median overall survival
• Kaplan Meier

Putting It In Perspective

Sometimes using median survival is misleading or not very useful. For instance, if you see a median survival reported for non-Hodgkin lymphoma or NHL, this refers to people with very different diseases, all mixed together in one statistic. NHL has many types and subtypes and prognoses and disease characteristics that can vary a lot from type to type.

When researchers talk about survival, there are some important truths to keep in mind. Generally, the study of a group of people does not use dates in the sense that we are used to, in a calendar: a person who entered a study in 2015 and person who entered a study in 2016 both have a “day zero,” which is their first day on the study.

At time zero, all patients are alive, so survival is 100 percent. Whenever a person dies, the percentage of surviving patients decreases. Now, all of us die eventually, so if you were looking at a survival graph, and you extended the study long enough, survival would eventually drop to zero regardless of the disease of interest or its therapy.

When looking at an entire study — the entire survival curve — it’s hard to talk about the results of the study all at once, and that’s where median survival comes into play. The median is the middle value of any set of numbers, so median survival is how long it takes until half of the people in the study have died — or the time of which half are still living, depending on how you are looking at it.

Sometimes, when the study is complete, more than half of the people enrolled in the trial are still alive. In these cases, a longer observation time — that is, a five-year or 10-year survival — might be used instead.