Merck (MSD) has reported that the Phase III KEYNOTE-756 clinical trial of Keytruda plus chemotherapy for breast cancer met the primary endpoint of pathological complete response (pCR) rate.

The double-blind, randomised trial is assessing Keytruda, an anti-PD-1 therapy, plus chemotherapy as a neoadjuvant therapy subsequent to adjuvant treatment, comprising Keytruda, in combination with endocrine therapy.

The trial enrolled 1,240 individuals with early-stage, high-risk, oestrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) breast cancer.

Dual primary endpoints of the study are event-free survival (EFS) and pCR rate while overall survival and safety comprise the secondary endpoints.

According to data from an interim assessment conducted by the independent Data Monitoring Committee (DMC), the Keytruda regimen was shown to offer a statistically significant pCR improvement rate versus a neoadjuvant placebo and chemotherapy.

Keytruda’s safety profile in the trial was in line with that seen in earlier trials, and no new safety signals were detected.

As per the DMC guidance, the trial will be progressed without any modifications to analyse EFS.

Merck Research Laboratories global clinical development vice-president Dr Gursel Aktan said: “This is the first positive Phase III study evaluating an immunotherapy-based regimen for patients with high-risk, early-stage ER-positive, HER2-negative breast cancer, and an important milestone in our efforts to advance research in early-stage breast cancer.”

Keytruda has received approval in the US for two indications to treat triple-negative breast cancer patients.

Prior to this development, Merck reported positive topline findings from two Phase III trials of its investigational 21-valent pneumococcal conjugate vaccine, V116.