Pharmaceutical giant Merck & Co., Inc. — known internationally as MSD — has received U.S. regulatory approval for expanded use of its immunotherapy KEYTRUDA and the newer formulation KEYTRUDA QLEX in combination with paclitaxel, with or without bevacizumab, for adults with PD-L1–positive platinum-resistant ovarian, fallopian tube, or primary peritoneal cancer who have already undergone one or two prior systemic treatments.
The authorization from the U.S. Food and Drug Administration is based on results from the Phase 3 KEYNOTE-B96 study presented at the European Society for Medical Oncology Congress in 2025. In patients whose tumors expressed PD-L1, the regimen reduced the risk of disease progression or death by 28% and lowered the risk of death by 24% compared with chemotherapy alone.
Median progression-free survival reached 8.3 months with the Keytruda-based combination versus 7.2 months in the control group. Overall survival improved to 18.2 months compared with 14.0 months. The trial enrolled 643 patients, with most receiving bevacizumab and nearly half experiencing very rapid recurrence after platinum therapy.
Oncologists say the approval addresses a major treatment gap. Bradley Monk explained that once ovarian cancer becomes platinum-resistant, treatment options narrow dramatically and disease progression often accelerates.
Merck researchers emphasized the significance of introducing a PD-1 inhibitor in this setting. Gursel Aktan said the decision reflects years of clinical investment and opens the possibility of longer survival for patients facing historically poor outcomes.
The subcutaneous QLEX formulation demonstrated comparable pharmacokinetics, efficacy and safety to the intravenous therapy in supportive studies, enabling more flexible administration options.
Safety findings were consistent with known immunotherapy risks. Serious adverse reactions occurred in more than half of treated patients, including infections, adrenal insufficiency and pulmonary complications, while about 4% experienced fatal events. The most frequent side effects included diarrhea, fatigue, nausea, hair loss and peripheral neuropathy.
Despite safety considerations, specialists believe the approval marks a meaningful step toward combination immunotherapy strategies in women’s cancers. By pairing checkpoint inhibition with chemotherapy and anti-angiogenic therapy, clinicians may now have a more effective option for patients whose disease previously offered limited hope after resistance to platinum-based treatment.