Using Keytruda (pembrolizumab) in combination with chemotherapy increased the percentage of patients showing no signs of breast cancer after completing a course of neoadjuvant therapy — treatment to shrink a tumor — and  surgery, interim analysis of a Phase 3 trial shows. This marks the first time this type of therapy plus chemotherapy has demonstrated a statistically significant improvement in treating triple-negative breast cancer, the researchers said. Keytruda is a checkpoint blockade immunotherapy developed by Merck (known as MSD outside the U.S. and Canada), which has been approved by the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for treating several types of cancer. It is a monoclonal antibody that has been designed to target and block the activity of the PD-1 receptor — a protein found on the surface of immune cells — preventing cancer cells from avoiding being targeted and killed by immune cells. Monoclonal antibody treatments enlist the body's natural immune system functions to fight cancer. The ongoing randomized, double-blind, KEYNOTE-522 Phase 3 trial (NCT03036488) is assessing the safety and efficacy of Keytruda, versus a placebo, in combination with chemotherapy in 1,174 people with triple-negative breast cancer (TNBC). In the first part of the study, participants are randomly assigned to receive either Keytruda in combination with chemotherapy, or a placebo plus chemotherapy as a neoadjuvant therapy for approximately 24 weeks (eight cycles). Neoadjuvant therapy aims to reduce the tumor burden before it's removed by surgery. After completing a course of neoadjuvant therapy, participants undergo definitive surgery, followed by an additional treatment with Keytruda or a placebo as an adjuvant