For decades, the Food and Drug Administration’s accelerated approval pathway has helped companies get drugs for serious unmet medical needs to patients — and the market — sooner. But about half of cancer drugs approved via this route fail to improve patient survival or quality of life in subsequent clinical trials after more than five years of follow-up, according to new findings presented Sunday at the American Association for Cancer Research annual meeting.

The data come from an analysis of cancer drugs granted accelerated approval over the past decade. In some cases, failure to show clinical benefit didn’t stop the FDA from converting accelerated approvals into full approvals, and the authors note the agency’s conversion decisions have increasingly been based on less stringent evidence of a drug’s benefits.