HISTORICALLY, WOMEN HAVE BEEN less likely to be included in cancer clinical trials than men. Ensuring that clinical trials reflect the wider population is vital, because the biological attributes of a person’s sex can have an impact on the efficacy and safety profile of a new drug. If these differences can’t be observed during trials, they may contribute to disparities further down the line.

Over the past three decades, the National Institutes of Health (NIH) and the Food and Drug Administration (FDA) have set policies designed to increase the participation of women in clinical research, including the National Institutes of Health Revitalization Act of 1993, which directed the NIH “to establish guidelines for the inclusion of women and minorities in clinical research.” But it can be difficult to determine how effective these policies really are.

A group of researchers co-led by Shehara Mendis, a medical oncologist at Cabrini Health and Western Health in Australia, aimed to measure the effect of inclusivity guidelines on clinical research in a study published Sept. 22, 2020, in the Oncologist. They found that women are still underrepresented in U.S. cancer clinical trials, with worse representation in certain cancers, such as colorectal cancers. Mendis and her colleagues were surprised to see that representation of sex in cancer clinical trials differed by cancer type.

Mendis and senior study author Jonathan Loree, a medical oncologist at BC Cancer in Vancouver, British Columbia, spoke with Cancer Today about the study and why proportional representation in clinical trials benefits cancer patients. 

CT: Why did you do this study?
MENDIS: We’ve known for decades that sex is a social determinant of health, just like education level, socioeconomic status or race. There are biological differences between men and women that may impact cancer treatment. Yet for a long time, women were underrepresented in cancer research trials. We wanted to know: Are women getting the best possible cancer care or are they still potentially disadvantaged by sex? A number of policies have aimed to increase female representation in health research. Our goal was to create a report card to see how these policies are doing.

CT: How does underrepresentation in clinical research impact women seeking cancer care?
MENDIS: There are biological differences between men and women in how tumors grow, how the body processes drugs and how the immune system acts. For example, recent studies have shown that women on certain chemo regimens experience more nausea than men.
LOREE: If we know ahead of time that a certain drug or drug combo causes more side effects in one group, we can take steps before treatment to make the patient experience far better for people in that group. If cancer treatment studies focus mostly on men, we could be missing a whole bunch of effects and side effects in women.

CT: What did you find in your study?
MENDIS: We looked at the ratio of female to male participation in 186 clinical trials supporting 170 FDA cancer drug approvals between 2008 and 2018. We excluded sex-specific cancers including prostate, ovarian and breast cancers. We found that women are still underrepresented in clinical trials, and that this underrepresentation is worse in cancers involving solid organ tumors.
LOREE: Across all cancers, 3% fewer women participated in clinical trials than would be expected based on U.S. cancer incidence.
MENDIS: Three percent might not seem like a lot, but it represents thousands of cancer trial patients.

CT: How does sexual representation break down by cancer type?
MENDIS: Women were least proportionately represented in colorectal, pancreas, lung, kidney and thyroid cancer trials, while enrollment for women in leukemia and lymphoma cancer trials looked better. With colorectal cancer, for instance, 28% fewer women participated in clinical trials than would be expected based on the proportion of U.S. women that have that cancer type. In comparison, underrepresentation of women for leukemia trials was only 5%.

CT: Why are women still underrepresented in cancer research?
MENDIS: We don’t know. Previous studies have suggested that things like transportation difficulties, economic considerations and family responsibilities might be barriers to clinical trial participation.
LOREE: Future studies should focus on whether these barriers disproportionately affect women and how those barriers might differ by tumor type. Our goal as oncologists and researchers should be to make clinical research as accessible as possible to everyone.

CT: Where can our readers learn more about cancer clinical trials?
MENDIS: Start with a discussion with your oncologist about what trials may be available to you and whether you might be suitable for a particular trial. In the U.S., the National Cancer Institute’s Cancer Information Service can also provide a free, tailored clinical trials search that you can discuss with your doctor. To reach them, call 1-800-4-CANCER (1-800-422-6237 or visit their website).

This interview has been edited and condensed for clarity.