What Is a Kaplan-Meier Curve?
A Kaplan-Meier curve is a graph used to show survival over time. In oncology trials, Kaplan-Meier curves often show overall survival, progression-free survival, event-free survival or relapse-free survival.
What the curve shows
The vertical axis shows the percentage of patients who remain event-free. The horizontal axis shows time. The curve steps downward when events occur.
Why Kaplan-Meier curves matter
Median survival gives one point on the curve. Kaplan-Meier curves show the full pattern. They can reveal early benefit, delayed benefit, curve separation, curve crossing, long survival tail, early toxicity, loss of benefit over time and small number of patients at risk late.
Curve separation
If the treatment curve stays above the control curve, the treatment arm is doing better. If curves separate early and remain separated, that can be strong. If curves separate late, it may suggest delayed treatment effect. If curves cross, interpretation becomes more complicated.
Median survival on the curve
The median survival point occurs when the curve crosses 50%. If the curve has not crossed 50%, median survival is not reached.
Read more: What Does “Median Not Reached” Mean?
Hazard ratio and Kaplan-Meier curves
Hazard ratio summarizes relative event risk over time, but it may not fully capture curve shape.
Read more: Hazard Ratio Explained for Biotech Investors
Number at risk
Good Kaplan-Meier charts include a number-at-risk table below the graph. This shows how many patients remain under observation at each time point. Late parts of the curve can look impressive but may be based on very few patients.
Censoring marks
Censoring marks show patients who were still alive or event-free at last follow-up, lost to follow-up or otherwise did not have an event by analysis.
Read more: What Is Censoring in Clinical Trials?
What investors should look for
Ask whether curves separate, when they separate, whether they cross, whether benefit is consistent over time, how many patients remain at risk late, whether censoring is balanced, whether the median is reached and whether the result is clinically meaningful.
Bottom line
Kaplan-Meier curves show the shape of survival data. Do not rely only on median survival. Read the curve.