Merck’s Keytruda, with more than 40 approved indications, hasn’t yet been able to crack specifically into ovarian cancer. But with promising early results from a phase 3 study in certain patients, the checkpoint inhibitor may have found its place.

At a pre-specified interim analysis of Merck’s phase 3 Keynote-B96 trial, which is testing Keytruda plus chemotherapy with or without Roche’s Avastin in patients with platinum-resistant recurrent ovarian cancer, the drug showed “statistically significant and clinically meaningful” improvements in progression-free survival regardless of patients' PD-L1 status, Merck reported on Thursday.

The trial compared the Keytruda regimen against placebo and chemotherapy, again with or without Avastin.

Keynote-B96 enrolled a broad all-comers population with or without PD-L1 expression. In the PD-L1-positive subgroup, Keytruda was able to help patients live longer compared to the control regimen.

The results mark the first time a Keytruda-based regimen has been able to help certain patients with platinum-resistant ovarian cancer live longer, as well as the first time an immune checkpoint inhibitor-based regimen has demonstrated an overall survival benefit in ovarian cancer, Gursel Aktan, M.D., Ph.D., vice president of global clinical development at Merck Research Laboratories, pointed out in Merck’s release. 

“The positive results from this trial add to the growing body of evidence supporting the potential benefit of Keytruda across gynecological cancers, including this difficult-to-treat form of ovarian cancer for which patients are in need of new options,” Aktan added.

The company plans to present the results at an upcoming medical meeting and share them with regulatory authorities across the globe.

Ovarian cancer is the seventh most common cancer in women worldwide. This year is expected to see about 12,730 ovarian cancer-related deaths and some 20,890 diagnoses in the U.S. alone, according to Merck.

Keytruda, along with chemotherapy and followed by maintenance therapy with Merck’s AstraZeneca-partnered Lynparza, was previously evaluated as a first-line treatment for patients with BRCA non-mutated advanced epithelial ovarian cancer. Despite proving improvements in progression-free survival, the Keytruda-Lymparza combo couldn’t meet its overall survival endpoint, leaving Merck “uncertain” about the role of Keytruda in the indication, the company said at the time.

The challenge of PD-1 inhibitors in ovarian cancer doesn’t seem to be Keytruda-specific, as GSK’s Jemperli-Zejula combo regimen couldn’t significantly extend patients’ lives in first-line advanced ovarian cancer either last year. That’s because ovarian cancer is typically considered a “cold tumor,” meaning it doesn’t trigger a strong immune response and is therefore less responsive to immunotherapies such as checkpoint inhibitors. 

Elsewhere, Keytruda recently made waves in another tough-to-treat cancer type with groundbreaking results in late-stage resected, locally advanced head and neck squamous cell carcinoma. That trial marked the first positive one in two decades for that disease population, also making Keytruda the first PD-1 to achieve such a feat.