Despite 0% response rate, 4D hits primary endpoint in Keytruda combo trial, sending stock skyward

Can a 0% response rate represent success in an oncology clinical trial? Investors said yes on Wednesday, sending shares in 4D pharma up 30% after enough patients in its Keytruda combination trial had stable disease for the study to hit its primary endpoint.

To meet the primary endpoint in the second part of the kidney cancer trial, 4D needed to show that giving its microbiome therapy MRx0518 in combination with Keytruda provided clinical benefit to more than three out of 30 patients. The trial defined clinical benefit as complete response, partial response or stable disease for at least six months.

So far, 4D has enrolled 20 renal cell carcinoma (RCC) patients who previously progressed after treatment with an immune checkpoint inhibitor. Four of the first 16 evaluable patients had stable disease for at least six months after receiving MRx0518 in combination with Keytruda, causing the clinical trial to hit its primary goal. 

“Meeting the primary efficacy endpoint for this group is crucial for the future development of MRx0518, and these data are highly informative for our strategy going forward as we determine next steps in RCC,” Alex Stevenson, chief scientific officer at 4D, said in a statement. Investors agreed, sending shares in 4D up 30% to over $6 each in premarket trading.

The excitement reflects the early sign that 4D’s live biotherapeutic may be able to enhance the effects of checkpoint inhibitors. Some patients who previously progressed on a checkpoint inhibitor stabilized when they began taking daily capsules of MRx0518. Yet, in a field typically defined by evidence that interventions shrink tumors and prolong lives, success based on stable disease in four patients could be seen as slight.

4D is now preparing for further tests of its candidate. The British biotech plans to talk to its advisory board about the development path, including a potentially pivotal study in RCC patients who are refractory to immune checkpoint inhibitors.