Clinical trial results are published in medical journals, presented at conferences, and summarised on registries like ClinicalTrials.gov. For patients and caregivers trying to understand whether a treatment works, reading these results can be confusing. This guide explains the key concepts you need to know — endpoints, significance, effect size, and what the results actually mean for individual patients.
Primary and Secondary Endpoints
Every trial has a primary endpoint — the main question the study is designed to answer. In cancer trials, common primary endpoints include overall survival (how long patients live), progression-free survival (how long until the disease worsens), and objective response rate (how many patients see their tumours shrink).
Secondary endpoints measure additional outcomes, such as quality of life, duration of response, or specific side effects. A trial may meet its primary endpoint but not secondary ones, or vice versa. The primary endpoint is what determines whether the trial is considered a success.
Statistical Significance vs. Clinical Significance
A result is statistically significant if it is unlikely to have occurred by chance. This is expressed as a p-value — typically, a p-value less than 0.05 means the result is statistically significant.
However, statistical significance does not always mean the result matters clinically. A drug that extends survival by 2 weeks with a p-value of 0.01 is statistically significant, but a 2-week improvement may not be clinically meaningful — especially if the drug causes severe side effects.
Always look at the actual numbers (effect size), not just whether the result was significant.
Reading a Trial Summary
When you encounter trial results on a registry or in a news article, look for:
• The primary endpoint and whether it was met
• The magnitude of benefit (how much better was the treatment group?)
• The comparison group (what was the new treatment tested against?)
• The safety profile (what side effects occurred and how common were they?)
• The patient population (who was included in the trial — does it match your situation?)
• The sample size (larger trials produce more reliable results)
Be cautious about preliminary results, which may change as more data is collected.
What Results Mean for Individual Patients
Trial results describe averages across groups of people. A median overall survival of 14 months means half the patients lived longer than 14 months and half lived shorter — not that every patient will live exactly 14 months.
Your individual outcome depends on many factors not captured in the trial statistics, including your overall health, the specific characteristics of your disease, and how your body responds to treatment. Trial results are a guide, not a prediction.
Discuss results with your doctor, who can help interpret them in the context of your specific situation.
Frequently Asked Questions
What does "median overall survival" mean?
Median overall survival is the length of time at which half of the participants are still alive and half have died. For example, if the median overall survival is 12 months, half the participants lived longer than 12 months. It does not mean every patient will live exactly 12 months.
What is a hazard ratio?
A hazard ratio compares the rate of events (like death or disease progression) between two groups. A hazard ratio of 0.7 means the treatment group had a 30% lower rate of the event compared to the control group. Lower than 1.0 favours the treatment; higher than 1.0 favours the control.
Should I make treatment decisions based on trial results?
Trial results are important information, but treatment decisions should be made in consultation with your doctor, who can interpret results in the context of your specific medical situation, overall health, and treatment goals.