Young cancer patients who couldn’t get a key medicine because of a national drug shortage were more likely to suffer a relapse than others who were able to get the preferred treatment, doctors report. It’s the first evidence that a long-standing drug-supply problem may have affected cancer treatment results in specific patients.

The study involved more than 200 children and young adults with a blood cancer called Hodgkin lymphoma. Like childhood leukemia, it can be cured nearly 80 percent of the time. But a drug shortage that has worsened since 2009 is threatening that success rate, doctors report in Thursday’s New England Journal of Medicine.

Hundreds of drugs, including sedatives, antibiotics, painkillers and cancer treatments, have gone in and out of short supply in recent years.