Newswise — ARLINGTON, Va., October 27, 2020 — 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% of African Americans in the U.S. census and does not account for disproportionately higher rates of cancer incidence and death among African Americans. Asian American patients were also underrepresented in the trials relative to their population size. Findings will be presented today at the American Society for Radiation Oncology (ASTRO) Annual Meeting.

“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 Emily H. Bero, a medical student at the Medical College of Wisconsin in Milwaukee and lead author of the study. "Our study looks specifically at representation in radiation therapy trials."

Challenges with racial diversity in clinical trials are well established, for trials generally as well as those specific to cancer. A 2018 ProPublica analysis, for example, found that fewer than 5% of patients in trials for recently FDA-approved cancer drugs were Black, yet African Americans account for 13% of the U.S. population. Enrollment data from cancer trials indicates that inclusion of patients from racial/ethnic groups in those studies has gotten worse over time.

For the current analysis, researchers examined clinical trials involving radiation therapy that were posted from 1996 to 2019 on, a global database of trials that is maintained by the U.S. National Library of Medicine. A total of 122 trials (of 1,242 reviewed) met inclusion criteria, and researchers compared the percentages of different race groups in those trials with U.S. census estimates from 2018.

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 (i.e., Hispanic or Latino 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, an 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."

Incidence rates for prostate, colon, stomach, cervical and other cancers are higher for Black populations than for non-Hispanic white populations, and Black men have the highest cancer incidence rate of any group. African Americans also face the highest cancer death rates of any racial/ethnic group for all cancers combined and for many of the most common cancers.

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 gynecological cancers—and male-specific trials—those for prostate, penile and testicular cancers—had the most diverse racial composition (both p< 0.001; female-specific trials: 81% white, 13% Black, 5% Asian American, <1% other; male-specific trials: 80% white, 18% Black, 1% Asian American, 0% other). The trials involving proton therapy, an advanced but expensive type of radiation therapy, were the least diverse (p<0.001; 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 the disparity, 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."

While etiologies behind the disparities were beyond the scope of the current study, ASTRO's Committee on Health Equity, Diversity and Inclusion (CHEDI) outlined several barriers to trial participation in a 2019 blog post. Structural racism, distrust of medical providers, hidden costs associated with trial participation and a lack of community outreach by researchers all consistently limit inclusion of patients from underrepresented minority groups in cancer clinical trials. These obstacles call for solutions including improved diversity in the physician workforce, greater community involvement, such as partnering with community cancer centers, and more recruitment and support programs tailored to specific cultural backgrounds.

"Clinical trials are the mainstay in the development and validation of new cancer therapies and treatment options," wrote Fumiko Chino, MD, in the post. "As racial/ethnic minorities carry some of the highest cancer burdens in the United States, equitable participation in clinical trials becomes an important tool in the fight against health care disparities."


See this study presented:

  • Characterization of Underrepresented Populations in Modern Era Radiation Therapy Clinical Trials (Abstract 204).
  • Visit our press kit for a recording and more information.

The American Society for Radiation Oncology (ASTRO) is the world’s largest radiation oncology society , with more than 10,000 members who are physicians, nurses, biologists, physicists, radiation therapists, dosimetrists and other health care professionals who specialize in treating patients with radiation therapies. The Society is dedicated to improving patient care through professional education and training, support for clinical practice and health policy standards, advancement of science and research, and advocacy. ASTRO publishes three medical journals, International Journal of Radiation Oncology • Biology • Physics, Practical Radiation Oncology and Advances in Radiation Oncology; developed and maintains an extensive patient website, RT Answers; and created the nonprofit foundation Radiation Oncology Institute. To learn more about ASTRO, visit our website and follow us on our blog, Facebook, Twitter and LinkedIn.

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