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Are women underrepresented in cerebrovascular disease clinical trials? A systematic review using the FDA database

BACKGROUND AND PURPOSE: Clinical trials provide essential evidence in the US Food and Drug Administration (FDA) drug approval process. Women were underrepresented in the enrollment of clinical trials for many medical conditions other than cerebrovascular disease (CVD). We investigated women's participation in FDA-registered CVD-related interventional clinical trials and assessed whether women CVD patients in the United States were underrepresented. We also evaluated the association between the underrepresentation and the features of design and operation among these trials. METHODS: We systematically reviewed the phase 2 and 3 CVD-related interventional trials started between 2002 and 2017 in the FDA database. The proportions of women enrolled in these trials and the proportion-to-prevalence ratios (PPRs), defined as the ratios of the proportions of women enrolled in these trials to the proportion of women prevalent among US CVD patients during the same period, were calculated and summarized by a meta-analysis approach. We used boosted regression tree, a machine learning model, to identify the determinants of women's underrepresentation in CVD-related trials. RESULTS: According to our selection criteria, we analyzed the data of 145 CVD-related trials, among which 40.9% (95% CI: 38.3 - 43.5%) of the patients enrolled were women. Their PPR was estimated to be 0.843 (95% CI: 0.796 - 0.890). We found that four factors substantially influenced women's underrepresentation in these trials: the number of enrollment sites, the starting year, randomization, and academic institution sponsorship. CONCLUSIONS: Generally, women with CVD in the United States were underrepresented in FDA-registered trials started between 2002 and 2017. In addition, trials with greater numbers of enrollment sites, randomization, and non-academically sponsored trials had a higher risk of underrepresenting women with CVD in the United States. Investigators should take these factors into consideration in clinical trial design in the future, by either increasing women's participation or stratifying the enrollment by gender.