Merck has reported that the Phase III Keynote-119 trial evaluating its anti-PD-1 therapy Keytruda as a monotherapy to treat metastatic triple-negative breast cancer (TNBC) did not meet its pre-specified primary endpoint of superior overall survival (OS) compared to chemotherapy.

The company did not formally test other endpoints as the primary endpoint of OS was not met.

The secondary endpoints of the Keynote-119 Phase III randomised clinical trial are progression-free survival, overall response rate, disease control rate and duration of response.

As part of the study, a total of 622 patients were randomised to receive either Keytruda as a monotherapy or physician’s choice of single-agent chemotherapy at 1:1 ratio.

The study did not identify any new safety concerns.

Merck Research Laboratories chief medical officer, global clinical development senior vice-president and head Dr Roy Baynes said: “Metastatic triple-negative breast cancer is an aggressive and challenging disease to treat, especially after progression on initial standard-of-care treatment.

“While we are disappointed by the outcome of this monotherapy trial, we are continuing to study Keytruda in earlier stages of the disease and in combination with chemotherapy to address the unmet medical need of patients with triple negative breast cancer.”

The breast cancer clinical development programme covers several internal and external collaborative studies, including three ongoing registration-enabling studies Keynote-355, Keynote-242, and Keynote-522 in TNBC.

The anti-PD-1 therapy Keytruda increases the ability of the body’s immune system to help detect and fight tumour cells.

It blocks the interaction between PD-1 and its ligands, PD-L1 and PD-L2, and will activate T lymphocytes, which may affect both tumour cells and healthy cells.