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Study Finds Further Efforts Needed for Inclusion of Underrepresented Populations in Radiotherapy Clinical Trials


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A new study finds that the racial composition of clinical trials involving radiation therapy does not match that of the U.S. population. Examining trials from the past 23 years, researchers found that roughly 12% of trial participants were Black, which is less than the 13% population composition of Black people in the most recent U.S. census and does not account for disproportionately higher rates of cancer incidence and death among this population. Asian American patients were also underrepresented in the trials relative to their population size. These findings were presented at the 2020 American Society for Radiation Oncology (ASTRO) Annual Meeting (Abstract 204).

“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,” said lead study author Emily H. Bero, a medical student at the Medical College of Wisconsin in Milwaukee, in an ASTRO press release. “Our study looks specifically at representation in radiation therapy trials.”

Challenges with racial diversity in clinical trials are well established. A 2018 ProPublica analysis, for example, found that fewer than 5% of patients in trials for recently FDA-approved cancer drugs were Black, yet Black people account for 13% of the U.S. population. Enrollment data from cancer trials, reviewed by Duma et al in JCO Oncology Practice, indicated that inclusion of patients from racial/ethnic groups in those studies has decreased over time.

Analysis Methods and Findings

For the current analysis, researchers examined clinical trials involving radiation therapy that were posted from 1996 to 2019 on ClinicalTrials.gov. A total of 122 trials of 1,242 reviewed met inclusion criteria; researchers then compared the percentages of different racial groups in those trials with U.S. census estimates from 2018.

“There is a complex interplay of systemic barriers and other factors in clinical trial enrollment and participation. 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.”
— Emily H. Bero

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The racial composition of radiation therapy trials was 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 one race group. By comparison, the census figures were 72% White (12 percentage points lower than the trials), 13% Black (1 point higher than the trials), 6% Asian (3 points higher), and 9% from other races (8 points higher). Because race and ethnicity (ie, Hispanic or Latinx origin) are separate categories on the U.S. census, inclusion of Hispanic patients in clinical trials was not examined in the 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,” said senior author William A. Hall, MD, Associate Professor of Radiation Oncology and Surgery at the Medical College of Wisconsin. “There is still work to do in this regard, however, especially because some types of cancer disproportionately affect Black patients.”

The underrepresentation of Asian American patients was also surprising, said Dr. Hall. “Asian Americans have not been discussed extensively in research on disparities in clinical trial participation, but our findings signal that these discussions are needed.”

Researchers also examined racial diversity across different types of clinical trials. Female-specific trials—those for breast and gynecologic cancers—and male-specific trials—those for prostate, penile, and testicular cancers—had 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). Trials involving proton therapy were the least diverse (P < .001; 94% White, 6% Black, < 1% Asian American, 0% other).

An important limitation of this study is that is does not account for potential differences in how commonly cancer is diagnosed in different racial groups, explained Ms. Bero.

“Racial differences in incidence for certain types of cancer may explain the larger proportions of Black women and men in female-specific and male-specific radiation therapy trials,” she said. “This should also raise the consideration, however, that given these disparities in incidence, should the enrollment rates be even higher?”

Next steps for the researchers include expanding their focus to additional reasons behind disparities, such as socioeconomic status or characteristics of the trials themselves.

“There is a complex interplay of systemic barriers and other factors in clinical trial enrollment and participation,” explained Ms. 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.”

Disclosure: For full disclosures of the study authors, visit myastroapp2020.com.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
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