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JAMA Oncology Patient Page
December 2018

Clinical Trials, End Points, and Statistics—Measuring and Comparing Cancer Treatments in Practice

JAMA Oncol. 2018;4(12):1798. doi:10.1001/jamaoncol.2018.3708

What Are Cancer Treatment End Points?

Researchers use a set of established methods to compare one cancer treatment with another. Some of these measures define the ability of the treatment to inhibit cancer progression and improve patient outcomes, while others focus on adverse effects, safety, or treatment costs. Clinical trials are designed to identify one factor as the most important goal for the trial, which is its primary end point.

What Are Common Study End Points in Clinical Trials?

The earliest research in humans of a new drug or combination, a phase 1 study, explores the safety and tolerability of a treatment as drug dose is gradually increased. This process determines dose-limiting toxic effects, those frequent and severe enough to set the upper limit of dosing for future larger trials.

A phase 2 trial generally enrolls a few dozen patients treated with one approach or assigned at random (“randomized”) to 1 of 2 or more different treatments for their cancer. A phase 3 trial may randomize hundreds of patients to 1 or more novel treatments or to a control arm of patients receiving the best treatment available now, referred to as the standard of care.

There are several commonly used efficacy end points:

  • Objective response rate—the percentage of patients whose cancer shrinks to a specific degree, usually based on imaging assessments

  • Progression-free survival (PFS)—the proportion of patients who are alive and whose cancer does not progress on scans over a period from the start of the treatment

  • Overall survival (OS)—the proportion of patients still alive over a period from the start of the treatment

Statistics Let Us Describe Differences in Outcomes Between Groups

Results for different end points are compared in a few ways to assess whether one strategy is better than another. Differences are considered statistically significant if the probability of the differences seen occurring by chance, based on mathematical calculations, is below a threshold usually defined as 5%: this is also reflected as a P value of .05 or lower (1.00 representing 100% probability of chance explaining the findings).

Comparisons of the probability of tumor shrinkage are based on the difference in the proportion of patients achieving a response from different treatments.

The time-based end points of PFS and OS can be described by several measures. The median is the estimated time when half of the participants reach the measured event, disease progression or death, respectively. A landmark, such as 6-month PFS or 1-year OS, clarifies the percentage of patients who remain alive without progression or alive at these time points, respectively. A hazard ratio (HR) compares the risk of an event such as death or progression happening in one group vs another over time; it is usually expressed as a number between 0 and 1, in which the lower the value, the bigger the relative difference. For example, an HR of 0.62 represents a 38% improvement in risk of an event (1.00 − 0.62 = 0.38) in that end point with new treatment.

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Section Editor: Howard (Jack) West, MD.
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Article Information

Published Online: September 6, 2018. doi:10.1001/jamaoncol.2018.3708

Conflict of Interest Disclosures: None reported.