Racial Composition of Trials Involving RT Does Not Match Overall US Population

November 5, 2020
Hannah Slater
Hannah Slater

This study suggested that the racial composition of clinical trials involving radiation therapy does not match that of the overall US population.

According to study results presented at the American Society for Radiation Oncology (ASTRO) Annual Meeting, the racial composition of clinical trials involving radiation therapy (RT) does not match that of the overall US population.1

Specifically, the inclusion of Black patients in all RT specific clinical trials in the US nearly matched the US census composition with less than 1% variance (12.72 vs 11.83); however, this difference does not account for the disproportionately higher rates of cancer incidence and death typically observed among Black patients.

Moreover, Asian and other underrepresented populations had the largest magnitudes of difference. All differences were statistically significant though and were most pronounced in trials evaluating proton therapy.

“Clinical trials should reflect the diversity that exists in a population, yet we know challenges exist in both recruitment and retention of trial participants from racial minority groups. Understanding and minimizing disparities in clinical trials is critical to ensure health equity and the generalizability of research findings,” lead author Emily H. Bero, a medical student at the Medical College of Wisconsin in Milwaukee, said in a press release.2 "Our study looks specifically at representation in radiation therapy trials."

In this study, researchers evaluated clinical trials registered on clinicaltrials.gov involving RT with completed enrollment. Patient characteristics within each trial identified were examined; for trials without this data, individual publications were referred to. This data was then compared with data from the 2018 US census.

In total, 1242 clinical trials were reviewed, 122 met the study inclusion criteria, and 121 (99.1%) had race reported.

The racial composition of RT trials was found to be statistically different from the census estimates. Combined, the trials included 84% white patients, 12% Black patients, 3% Asian American patients, and less than 1% patients from other races (Native Hawaiian, Pacific Islander, American Indian, Alaskan native) or more than 1 race group. Comparatively, the census figures were 72% white, 13% Black, 6% Asian, and 9% from other races.

Importantly, given that race and ethnicity (ie, Hispanic or Latino origin) are separate categories on the US census, inclusion of Hispanic patients in clinical trials was not examined in the current study.

"We were surprised that the percentage of patients who are Black was not much lower than the census in terms of raw percentages, given the disparities and barriers that Black patients face in regard to clinical trials," senior author William A. Hall, MD, an associate professor of radiation oncology and surgery at the Medical College of Wisconsin, said in the release. "There is still work to do in this regard, however, especially because some types of cancer disproportionately affect Black patients."

Additionally, the investigators also evaluated racial diversity across different types of clinical trials. Female-specific trials (those for breast and gynecological cancers) and male-specific trials (those for prostate, penile and testicular cancers) were found to have the most diverse racial composition (both P < .001; female-specific trials: 81% white, 13% Black, 5% Asian American, <1% other; male-specific trials: 80% white, 18% Black, 1% Asian American, 0% other). However, trials involving proton therapy were shown to be the least diverse (P < .001; 94% white, 6% Black, <1% Asian American, 0% other).

Of note, an important limitation of this study is that it does not account for potential differences in how commonly cancer is diagnosed in different racial groups. Moving forward, the researchers intend to examine the different reasons behind the observed disparities, such as socioeconomic status or characteristics of the trials.

"There is a complex interplay of systemic barriers and other factors in clinical trial enrollment and participation," explained Bero. "The choices individuals and institutions make when designing clinical trials can also exacerbate or mitigate disparities—issues such as how rigid a trial's inclusion criteria are, where patients can find information about the trial and whether there is financial support for participation, as well as the implicit biases that shape these choices."


1. Bero EH, Rein L, Banerjee A, et al. Characterization of Underrepresented Populations in Modern Era Radiation Therapy Clinical Trials. Presented at the American Society for Radiation Oncology (ASTRO) Annual Meeting. Abstract #: 204.

2. Study finds need for better inclusion of patients from racial minority groups in radiation therapy trials [news release]. Arlington, Virginia. Published October 27, 2020. Accessed November 2, 2020. https://www.astro.org/News-and-Publications/News-and-Media-Center/News-Releases/2020/Study-finds-need-for-better-inclusion-of-patients