In colon and lung cancer trials, women were less likely to be enrolled than men, and at all study sites, the rates of participation in trials was extremely low, from 0.04 to 1.7 percent.

Dr. John H. Stewart IV, the lead author and an assistant professor of surgery at Wake Forest University, said the disparities could call the results into question. “Our ability to generalize the findings of surgical trials,” he said, “is directly dependent on having equitable participation in trials by underrepresented groups.”