Conference Coverage

A farewell to arms? Drug approvals based on single-arm trials can be flawed



If results of phase 3, randomized clinical trials are the gold standard for cancer drug approvals, then single-arm trials are at best a bronze or even brass standard, with results that should only be used, under certain conditions, for accelerated approvals that should then be followed by confirmatory studies.

In fact, many drugs approved over the last decade based solely on data from single-arm trials have been subsequently withdrawn when put through the rigors of a head-to-head randomized controlled trial, according to Bishal Gyawali, MD, PhD, from the department of oncology at Queen’s University, Kingston, Ont.

“Single-arm trials are not meant to provide confirmatory evidence sufficient for approval; However, that ship has sailed, and we have several drugs that are approved on the basis of single-arm trials, but we need to make sure that those approvals are accelerated or conditional approvals, not regular approval,” he said in a presentation included in a special session on drug approvals at the European Society for Medical Oncology Congress.

“We should not allow premature regular approval based on single-arm trials, because once a drug gets conditional approval, access is not an issue. Patients will have access to the drug anyway, but we should ensure that robust evidence follows, and long-term follow-up data are needed to develop confidence in the efficacy outcomes that are seen in single-arm trials,” he said.

In many cases, single-arm trials are large enough or of long enough duration that investigators could have reasonably performed a randomized controlled trial (RCT) in the first place, Dr. Gyawali added.

Why do single-arm trials?

The term “single-arm registration trial” is something of an oxymoron, he said, noting that the purpose of such trials should be whether to take the drug to a phase 3, randomized trial. But as authors of a 2019 study in JAMA Network Open showed, of a sample of phase 3 RCTs, 42% did not have a prior phase 2 trial, and 28% had a negative phase 2 trial. Single-arm trials may be acceptable for conditional drug approvals if all of the following conditions are met:

  • A RCT is not possible because the disease is rare or randomization would be unethical.
  • The safety of the drug is established and its potential benefits outweigh its risks.
  • The drug is associated with a high and durable overall or objective response rate.
  • The mechanism of action is supported by a strong scientific rationale, and if the drug may meet an unmet medical need.

Survival endpoints won’t do

Efficacy endpoints typically used in RCTs, such as progression-free survival (PFS) and overall survival (OS) can be misleading because they may be a result of the natural history of the disease and not the drug being tested, whereas ORRs are almost certainly reflective of the action of the drug itself, because spontaneous tumor regression is a rare phenomenon, Dr. Gyawali said.

He cautioned, however, that the ORR of placebo is not zero percent. For example in a 2018 study of sorafenib (Nexavar) versus placebo for advanced or refractory desmoid tumors, the ORR with the active drug was 33%, and the ORR for placebo was 20%.

It’s also open to question, he said, what constitutes an acceptably high ORR and duration of response, pointing to Food and Drug Administration accelerated approval of an indication for nivolumab (Opdivo) for treatment of patients with hepatocellular carcinoma (HCC) that had progressed on sorafenib. In the single-arm trial used as the basis for approval, the ORRs as assessed by an independent central review committee blinded to the results was 14.3%.

“So, nivolumab in hepatocellular cancer was approved on the basis of a response rate lower than that of placebo, albeit in a different tumor. But the point I’m trying to show here is we don’t have a good definition of what is a good response rate,” he said.

In July 2021, Bristol-Myers Squibb voluntarily withdrew the HCC indication for nivolumab, following negative results of the CheckMate 459 trial and a 5-4 vote against continuing the accelerated approval.

On second thought ...

Citing data compiled by Nathan I. Cherny, MD, from Shaare Zedek Medical Center, Jerusalem, Dr. Gyawali noted that 58 of 161 FDA approvals from 2017 to 2021 of drugs for adult solid tumors were based on single-arm trials. Of the 58 drugs, 39 received accelerated approvals, and 19 received regular approvals; of the 39 that received accelerated approvals, 4 were subsequently withdrawn, 8 were converted to regular approvals, and the remainder continued as accelerated approvals.

Interestingly, the median response rate among all the drugs was 40%, and did not differ between the type of approval received, suggesting that response rates are not predictive of whether a drug will receive a conditional or full-fledged go-ahead.

What’s rare and safe?

The definition of a rare disease in the United States is one that affects fewer than 40,000 per year, and in Europe it’s an incidence rate of less than 6 per 100,000 population, Dr. Gyawali noted. But he argued that even non–small cell lung cancer, the most common form of cancer in the world, could be considered rare if it is broken down into subtypes that are treated according to specific mutations that may occur in a relatively small number of patients.

He also noted that a specific drug’s safety, one of the most important criteria for granting approval to a drug based on a single-arm trial, can be difficult to judge without adequate controls for comparison.

Cherry-picking patients

Winette van der Graaf, MD, president of the European Organization for the Research and Treatment of Cancer, who attended the session where Dr. Gyawali’s presentation was played, said in an interview that clinicians should cast a critical eye on how trials are designed and conducted, including patient selection and choice of endpoints.

“One of the most obvious things to be concerned about is that we’re still having patients with good performance status enrolled, mostly PS 0 or 1, so how representative are these clinical trials for the patients we see in front of us on a daily basis?” she said.

“The other question is radiological endpoints, which we focus on with OS and PFS are most important for patients, especially if you consider that if patients may have asymptomatic disease, and we are only treating them with potentially toxic medication, what are we doing for them? Median overall survival when you look at all of these trials is only 4 months, so we really need to take into account how we affect patients in clinical trials,” she added.

Dr. van der Graaf emphasized that clinical trial investigators need to more routinely incorporate quality of life measures and other patient-reported outcomes in clinical trial results to help regulators and clinicians in practice get a better sense of the true clinical benefit of a new drug.

Dr. Gyawali did not disclose a funding source for his presentation. He reported consulting fees from Vivio Health and research grants from the American Society of Clinical Oncology. Dr. van der Graaf reported no conflicts of interest.

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