MSD has announced that its anti-PD-1 therapy Keytruda has failed to meet its primary endpoint in a late-stage study testing the drug as a standalone treatment in patients with metastatic triple-negative breast cancer (TNBC).

The blockbuster drug did not meet its pre-specified primary endpoint of superior overall survival in the Phase III KEYNOTE-119 trial, compared to chemotherapy such as capecitabine, eribulin, gemcitabine or vinorelbine.

The drug works by increasing the ability of the body’s immune system to help detect and fight tumour cells, and blocks the interaction between PD-1 and its ligands, PD-L1 and PD-L2, thereby activating T lymphocytes which may affect both tumour cells and healthy cells.

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

He continued, “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. We are grateful to the patients and investigators for their participation in this important study.”

TNBC is an aggressive type of breast cancer that characteristically has a high recurrence rate within the first five years after diagnosis. While some breast cancers may test positive for oestrogen receptor, progesterone receptor or human epidermal growth factor receptor 2 (HER2), TNBC tests negative for all three. As a result, TNBC does not respond to therapies targeting these markers, making it more difficult to treat. Approximately 10-20% of patients with breast cancer are diagnosed with TNBC.