Participation in a clinical trial is often considered something of an equalizer in medicine. Researchers have pushed for better access to trials for historically disadvantaged populations, hoping that increasing diversity in trials will both advance medicine and also help close health disparities by providing more equitable access to high-quality care.

But a new study suggests that increasing trial diversity won’t be enough to eliminate health disparities. The study, published in JAMA Network Open on Wednesday, found that even among clinical trial participants, disparities still emerged for some groups of breast cancer patients, including young Black and Hispanic patients and Hispanic patients with certain breast cancer subtypes.


“The study helps one to realize that even if we address one issue of access, there’s still other factors that we need to address with regard to eliminating disparities,” said Arnethea Sutton, a cancer disparities researcher at Virginia Commonwealth University who did not work on the study. “Just because patients have access to trials does not mean their outcomes are going to be the same because there are other factors outside of access to trials that contribute to outcomes.”

To do the study, researchers analyzed patient data from four completed clinical trials on breast cancer. “These were trials that began years ago, and people continued to be followed up to understand outcomes after the trial,” said Erica Warner, a cancer epidemiologist at Massachusetts General Hospital and the senior author on the study. That allowed Warner to study whether certain patients tended to do better or worse than other demographic groups long after the trial ended.

The analysis included 9,479 patients, sorted by racial and ethnic group, BMI, age, and breast cancer subtype. Of those, Warner found two key disparities emerged. Overall, Black and Hispanic patients under the age of 50 had worse survival than white patients under 50, and older Hispanic women with hormone receptor positive, HER2 negative cancers had a rate of recurrence that was considerably higher than white patients.


Clinical trial participants tend to already be more homogenous than patients in the real world, Warner added, because trials often have strict inclusion criteria, often ruling out patients with certain comorbidities or other conditions. “It means that these groups of people, be it Black, white, or Hispanic, are more similar to each other because there’s that selection to get into a trial,” she said. “It’s possible that outside of a trial setting, the differences we observed would be bigger.”

It also suggests that despite selecting more similar patients to start with, being on a clinical trial still wasn’t enough to eliminate disparities. “Why isn’t just being in a trial enough?” Warner said. “It’s because we don’t come into trials as blank slates. We have experienced the harms of systemic racism, and we bring that in our bodies into the trial. And then, trials don’t last forever.”

Many researchers hypothesize that patients often get better care on trials because they’re typically conducted at high-quality institutions, and their health is closely followed for the duration of the trial. But once that ends, the patients return to the “real world,” where, Warner said, they may face social, economic, and racial inequities that might affect their health. “All these things continue after the trial,” she said.

One example might be in adherence to endocrine therapy after breast cancer treatment for people with hormone receptor positive cancers, VCU’s Sutton pointed out. Endocrine therapy can help prevent recurrences of breast cancer, but only if the patient stays on it. Biological, social, or financial reasons can all influence whether a patient is able to keep taking the medication, Sutton said.

“There are studies on racial differences in adherence. Are women able to take the medicine in the way it’s prescribed? Black women tend to show more side effects than white women,” she said. “There could be biological drivers of this. It could be the environment. It could be that some women feel more comfortable reporting side effects, so they get handled. These disparities are multileveled, which is why we need multilevel solutions.”

Even if diversity in clinical trials can’t solve disparities on their own, they are still part of this solution, Warner said. “If we had more people in trials and more trials, it could help. One way is accelerating therapeutic innovation,” she said. “Another is optimizing therapeutic regimes. When you don’t have representation in trials, you design therapeutics and regimens that are only optimized for the population you’re studying. You miss variation in the trial if it’s not represented.”