Roughly a fifth of cancer clinical trials fail to recruit enough participants, creating a “major barrier to progress” for developing new therapies, according to a paper published in the Journal of the National Cancer Institute.

After reviewing information from 787 Phase 2/3 studies sponsored by the National Clinical Trials Network, experts from the University of Washington and Fred Hutchinson Cancer Center found that 145, or 18 percent, closed with low accrual or accrued at less than 50 percent of the target three or more years after opening, according to the paper.

The researchers identified a number of factors to help predict low trial accrual, such as competition from other clinical studies, a low annual incidence, higher risk for toxicity, greater trial complexity and longer follow up.

They say their future work will focus on the development of prediction tools in trial design, with an eye toward helping drugmakers appropriately target medical research, protecting limited resources.

The reviewers also say that more research will be needed in future to look at how the risk-factor model can affect decisions on clinical cancer studies.