Clinical Trial Endpoints in Cancer Research: Four Terms You Should Know

In recent years, we have made remarkable progress in cancer research. The latest discoveries have resulted in cutting-edge therapies that treat cancer in more sophisticated ways than conventional treatments like chemotherapy. Innovative treatments that target specific mutations harbored by cancer cells or help activate the body’s immune system to fight cancer are giving patients new options and improved outcomes.

At AstraZeneca, our scientists are at the forefront of groundbreaking research, bringing us closer to our goal of one day eliminating cancer as a cause of death. At each stage of development, we’re conducting clinical trials to assess a drug’s safety and effectiveness to ensure patients receive the most benefit.

Clinical trials in oncology have their own unique terminology, including endpoints, which are results that are measured at certain points during a study and/or at the completion of a study to see if a given medication has worked (e.g., did the drug demonstrate a significant improvement versus the comparative treatment?) and its safety (e.g., what are the possible side effects?). The U.S. Food and Drug Administration (FDA) uses study endpoints to inform drug approval decisions, while patients and physicians use endpoints to inform treatment decisions.

It is important for patients to stay informed and understand the latest discoveries, including results from clinical trials, to have productive conversations with their doctors, and ensure that they know the right questions to ask throughout their journey. Below are descriptions of some of the endpoints that are often measured in oncology clinical trials.


Overall Survival (OS)

Overall survival, or OS, measures how long patients, who undergo a certain treatment regimen, live compared to patients who are in a control group (i.e., taking either another drug or an inactive treatment, known as a placebo). If a clinical trial demonstrates improved OS, it provides evidence of the drug’s value in prolonging a cancer patient’s life. OS is a strong and precise endpoint, as it requires having more patients and longer follow-ups compared to other clinical trial endpoints. Given all this, OS is often considered the “gold standard” for measuring the clinical benefits of a cancer drug.


Progression-Free Survival (PFS)

Another important endpoint for measuring the effectiveness of cancer drugs is progression-free survival, or PFS – how long a person lives without the disease worsening. PFS results are typically available earlier in a trial than OS data. PFS is considered an indication of disease control and stabilization.


Overall Response Rate (ORR)

Overall response rate, or ORR, is the proportion of patients in a trial whose tumor is destroyed or significantly reduced by a drug. ORR is generally defined as the sum of complete responses (CRs) – patients with no detectable evidence of a tumor over a specified time period – and partial responses (PRs) – patients with a decrease in tumor size over a specified time period. Improved ORR offers tangible proof that the drug is working.  


Duration of Response (DoR)

Duration of response, or DoR, is the length of time that a tumor continues to respond to treatment without the cancer growing or spreading. Cancer drugs that demonstrate improved DoR can produce a durable, meaningful delay in disease progression, as opposed to a temporary response without any lasting benefit.



Determining the Path Forward                                 

If you receive a cancer diagnosis, it is important to work closely with your doctor to understand clinical trial endpoints and how they relate to treatment decisions throughout your cancer journey. With greater knowledge and better discussions with your doctor, you’ll have better chances to get the right treatment for your unique needs. Some good questions to ask a doctor may include:

  • What type of cancer do I have? What stage is it?
  • Is my cancer resectable (operable)? How might the possibility to operate impact my treatment course?
  • What types of treatments are appropriate for my specific type of disease?
  • What were the clinical trial results for the treatments you recommend for me?
  • Are there specific tests that may help identify which treatment options are most appropriate for my disease?


US-22163 Last Updated 9/18