Merck has reported positive results from the Phase III KEYNOTE-522 clinical trial of Keytruda in combination with chemotherapy for the treatment of triple-negative breast cancer (TNBC).

The study met one of its dual-primary endpoints, demonstrating a statistically significant improvement in pathological complete response (pCR) rates compared to chemotherapy alone.

These improvements were observed after completion of the neoadjuvant portion of the neoadjuvant/adjuvant regimen and were independent of patients’ PD-L1 status.

pCR is defined as a lack of all cancer signs in tissue samples assessed following neoadjuvant therapy and definitive surgery.

An independent Data Monitoring Committee (DMC) analysed the trial’s interim data and recommended its continuation to investigate the remaining dual-primary endpoint of event-free survival (EFS).

Safety analysis showed consistency with previously reported studies of Merck’s drug, without any new safety signals.

Merck Research Laboratories president Dr Roger Perlmutter said: “These findings from this innovatively designed trial with Keytruda mark the first time an anti-PD-1 therapy plus chemotherapy has demonstrated a statistically significant improvement in pathological complete response rate as a neoadjuvant, or pre-surgical, segment of treatment for TNBC.

“We are encouraged by these results and plan to discuss these data with health authorities and to present these findings at an upcoming medical congress.”

Keytruda is an anti-PD-1 therapy indicated for a variety of cancers, including non-small cell lung cancer (NSCLC), head and neck cancer, and Hodgkin lymphoma.

The randomised, double-blind KEYNOTE-522 study is comparing Keytruda plus chemotherapy with placebo plus chemotherapy as neoadjuvant treatment.

This will be followed by a comparison of the drug with placebo as adjuvant therapy. A total of 1,174 patients have been enrolled into the study.

In addition to the dual-primary endpoints, the trial will measure secondary endpoints, including pCR rate at the time of definitive surgery, EFS in patients with PD-L1-expressing tumours, overall survival, safety, and patient-reported outcomes.