The U.S. health regulator on Friday proposed cancer drug developers in most cases conduct more rigorous trials to seek accelerated approval for their candidates.

The Food and Drug Administration's proposed recommendation follows criticism for the accelerated approval pathway, as well as an independent federal review into it after the controversial nod for Biogen Inc's Alzheimer's treatment Aduhelm.

Accelerated approvals allow quicker nod for therapies that target serious and life-threatening conditions.

The FDA proposed using "randomized controlled trials" (RCT) where patients receive either a therapy or another alternate treatment, compared to conducting a trial testing the drug without a comparator, known as single-arm studies.

Single-arm studies can be conducted in some cases, but those need to be discussed with the agency beforehand, it said.

"Given the limitations of single-arm trials, a randomized controlled trial is the preferred approach to support an application for accelerated approval," the FDA said.

Drug developers usually depend on such "single-arm" studies to gain accelerated approval, and then conduct another trial post-nod to confirm clinical benefits.

The regulator suggested two approaches - one of conducting one RCT each before getting the accelerated nod and then to confirm the benefits, and another of holding just a single trial to seek the nod and then follow-up over the long term.

The single RCT approach will be advantageous as it can also provide a quicker verification of the benefits, the FDA said.

In the past few years, Merck's Keytruda was pulled as a treatment for certain lung cancer patients, and TG Therapeutics' lymphoma drug was withdrawn. Those accelerated approvals were based on single-arm studies.