Event-Free Survival (EFS) After Treatment

Event-free survival (EFS) is a term that denotes the possibility of having a particular group of defined events (could be a fracture, some lab test abnormality, a particular kind of progression like brain metastasis, etc.) after a treatment that is designed to delay or prevent that group of events.

A doctor and her patient talking together

Event-free survival is calculated when a particular treatment is given that is directed not towards improving survival, but to prevent or delay specific complications of the disease. It is a statistic often reported in clinical trials to compare new treatments to established treatments.

The term isn’t referring to whether the patients are still alive, but rather that they are alive and didn’t have a specific symptom or complication in the time period.


Please note that this is not an actual statistic, but is shown only as an illustration.

  • “The 1-year event-free survival for bone pain resulting from bone involvement by lymphoma after treatment with radiotherapy is 50%.”

This means that 50% of patients treated with radiotherapy for bone involvement are free from the event (bone pain) 1 year after treatment.

  • “Intensive dosing with imatinib, in addition to dose-intensive ALL chemotherapy more than doubled the 3-year event-free survival for children and adolescents with Ph+ ALL, with minimal toxicities.”

This quote from a research paper means that this course of therapy was twice as effective as the usual acute lymphoblastic leukemia chemotherapy in preventing events by the three-year mark of the study.

When event-free survival is reported, the term has five parts:

  1. The disease or condition being treated, such as lymphoma.
  2. The treatment that was given, such as radiotherapy.
  3. The time frame being reported, such as one year after treatment.
  4. The type of event being monitored for, such as bone pain.
  5. The percentage of patients who did not experience that event in that time frame, such as 50%.

No Events Is Good News

Like the curse, “May you live in interesting times,” having an event after treatment is bad news. No events and no news is good news. Being event-free can mean that the cancer being treated does not recur. It could mean that there is no bone pain from cancer that has spread to the bone.

A higher percentage of patients remaining event-free shows that a treatment is more effective. A treatment with 75% event-free survival is better than one with 25% event-free survival in that time frame.

A longer time frame is also better. Two procedures or treatments may be compared at one year, two years, five years, etc. with their rates of event-free survival for each time period.

What Event-Free Survival Doesn’t Tell You

This statistic doesn’t predict your life expectancy with the disease. It doesn’t mean that those who survived event-free were cured. They still have the condition. It doesn’t mean they don’t have other complications or progression of their illness; it refers to a specific event rather than events in general.

By Indranil Mallick, MD
 Indranil Mallick, MD, DNB, is a radiation oncologist with a special interest in lymphoma.