There was a very sobering piece in NEJM by the FDA last month in which the authors try to explore what went wrong with the Keynote-183, Keynote-185 and checkmate 602 trials testing PD-1 inhibitors combinations with pomalidomide or lenalidomide and dexamethasone in multiple myeloma. Interim analysis of Keynote 183 and 185 revealed detrimental effects on overall survival (OS) with hazard ratios of 1.61 and 2.06, not explained by differences in toxicities alone. The checkmate 602 trial was also halted in light of these findings and also showed higher mortality in the nivolumab combination arm.
In the thoughtful NEJM piece, the authors make at least three important points. First, they question why these PD-1 inhibitors were tested in combination despite their having limited single-agent activity. In fact, a couple of years ago, Vinay Prasad and I asked the same question: why are novel cancer drugs being tested in combination despite having limited activity as a single agent? We found that these drugs, even when ultimately approved, provide relatively low value and recommended that drugs with poor single agent activity not be tested in combinations unless there are specific reasons to expect synergy.
The second important point in the article is that many cancer drug approvals are lately based on durable response rates in single arm trials without a control group, a situation in which it is difficult to evaluate the safety and efficacy of drug combinations. Indeed, without an RCT, the oncology community would never have known these signals of detrimental effect. If the FDA had approved these PD-1 inhibitors in multiple myeloma on the basis of non-randomized trials, which it often does in other oncology contexts, who knows how long it would have taken to recognize the increased mortality in patients—and at what cost. This is another reason why we need RCTs more now than ever. Finally, the authors point out that these PD-1 inhibitors in multiple myeloma were directly advanced to phase 3 trials after phase 1 trials were completed, without phase 2 information. Indeed, in a recent paper, Alfredo Addeo and I showed that a substantial percentage of drugs that fail in phase 3 trials do not have supporting phase 2 data.