Women are under-represented in major clinical trials for cancers that affect both sexes, a new review finds. The trials include, on average, just 38.8 percent women.

The findings, which involve 2006 data, were announced today and are detailed in the July 15 issue of Cancer, a journal of the American Cancer Society.

"Only by understanding the forces affecting the sex distribution of study subjects can we as a society succeed in ensuring that our medical research efforts are inclusive and to the benefit of all," the authors conclude.

In 1993, the National Institutes of Health called for clinical trials to include adequate representation of women. The goal appears not to have been met.

In the new study, Dr. Reshma Jagsi of the University of Michigan in Ann Arbor and colleagues reviewed cancer clinical research appearing in eight highly regarded journals in 2006. These journals included the New England Journal of Medicine, JAMA, the Lancet, the Journal of Clinical Oncology, the Journal of the National Cancer Institute, Lancet Oncology, Clinical Cancer Research, and Cancer.

The analysis reviewed 661 prospective clinical cancer studies that enrolled more than a million participants. For each of the seven non-sex-specific cancer types assessed, the majority of studies enrolled a lower proportion of women than the proportion of women with that type of cancer in the general population. Non-sex-specific cancers included hematologic (blood-related), gastrointestinal, urinary, lung, nervous system, and head and neck cancers, as well as sarcomas (connective tissue–related). On average, women constituted 38.8 percent of patients enrolled in a study.

Women made up a significantly lower proportion of studies that focused on treatment for six of the seven non-sex-specific cancer types (excluding hematologic cancers).

The investigators also assessed differences between studies funded privately (such as by drug companies) vs. those relying on government funding. The latter had a higher percentage of female participants than those that were supported by private funds (41.3 percent vs. 36.9 percent).

This suggests that government policies may encourage more balance when enrolling men and women in clinical studies, the authors write. There also may be differences in review processes, grant size, or priorities associated with research funded by the government compared with those supported by industry.

According to the authors, future research should investigate why fewer women are enrolled in most cancer clinical studies. Barriers that may discourage women from research participation could include lack of information, fear, and perceived interference with personal responsibilities such as childcare. Also, some study investigators may be concerned with protecting women of childbearing age and may wish to limit their exposure to investigational medical interventions.

  • 5 Myths about Women's Bodies