Sellas retunes leukemia trial as patients live longer than expected. Is the biotech's drug behind survival boost?

Patients are living longer than expected in Sellas Life Sciences’ phase 3 trial for an acute myeloid leukemia (AML) drug. That’s great news for patients and has spurred a protocol amendment for the study—but the question remains: Is it because of the biotech’s drug?

The short answer is executives don’t know. The data have yet to be unblinded, and the analysis that led to the change in the main endpoint was pooled, meaning patients who received the treatment were lumped in with those in the control arm.

“I'm very excited that patients are living longer than expected,” said Sellas CEO Angelos Stergiou, M.D., on a Monday morning investor call.

Sellas’ galinpepimut-S, or GPS, is being tested in the late-stage REGAL study featuring patients with AML who have achieved complete remission after second-line salvage therapy. The main goal is overall survival, which is a measure of how many patients are still alive after treatment begins.

What the company does know is that patients are surviving “considerably longer” than their previous assumptions about the typical course of AML. After consultation with the independent data monitoring committee, Sellas is implementing a number of changes to the trial, including raising the enrollment target from 116 patients up to a range of 125-140.

Sellas has reduced the targeted number of deaths for the interim analysis from 80 down to 60, which is expected to occur in late 2023 or 2024. The number of deaths for the final analysis has been cut from 105 to 80, which Sellas expects to occur by the end of 2024. Finally, the bar for statistical significance has been altered to 12.6 months overall survival compared to eight months for patients on best available care, which is the control arm of the trial.

“Although I cannot speculate, personally I do believe and hope for really the entire leukemia space that GPS is the driver but again, unless and until we unblind the data we don't know and obviously we're very excited to do that here very soon,” Stergiou said.

Reducing the number of deaths needed for analysis will allow for faster completion while keeping the study sensitive to the drug’s potential effect, Stergiou said.

In a previous phase 2 trial, Sellas reported a 16-month difference between patients receiving GPS and those on best available therapy. Patients receiving GPS achieved overall survival of 21 months compared to 5.4 months in the control arm.

While one possibility is that Sellas’ therapy is performing well, the flip side is that the control side could be seeing a surge in responses, too. The trial uses best available treatment as the control, meaning patients receive common approved therapies for AML. Among the best available treatments used in the trial is Genentech and AbbVie's Venclexta. 

Either way, Stergiou called the trial changes a positive step toward achieving a maintenance therapy for this type of advanced AML, which has an unmet need.

“If patients would have died earlier, our discussion today would have been different,” he said. “To the extent that we can and that I can be, I'm very hopeful that GPS is driving the survival benefit.”

The bottom line is that the study is going to take longer to complete than planned. Investors had pushed Sellas’ shares down 45% by 11 a.m. ET on Monday. The company was trading at $2.48, down $2.07 compared to $4.55 at the previous close.

In other news, Sellas’ Chinese partner company 3D Medicines has joined the study and will bring on about 20 patients from the greater China region. This has been made possible by the expansion of the enrollment target and means Sellas is up for a milestone payment that should arrive in the second half of 2023.

GPS is Sellas’ lead asset in a pipeline that also has GFH009, which is in phase 1 testing for hematologic malignancies. The company is also developing GPS in mesothelioma, multiple myeloma and ovarian cancer.