Merck announced the final overall survival results from the pivotal Phase 3 KEYNOTE-355 trial investigating KEYTRUDA, Merck’s anti-PD-1 therapy, in combination with chemotherapy (paclitaxel, nab-paclitaxel or gemcitabine/carboplatin) for the first-line treatment of patients with metastatic triple-negative breast cancer (mTNBC). KEYTRUDA is the first anti-PD-1 therapy in combination with chemotherapy to demonstrate a statistically significant and clinically meaningful improvement in OS for these patients. In this study, KEYTRUDA plus chemotherapy reduced the risk of death by 27% (HR=0.73 [95% CI, 0.55-0.95]; p=0.0093) in patients with mTNBC whose tumors expressed PD-L1 (Combined Positive Score [CPS] =10), as compared to chemotherapy alone. There was an increase of 6.9 months in median OS with KEYTRUDA plus chemotherapy compared to chemotherapy alone (23.0 months [95% CI, 19.0-26.3] vs. 16.1 months [95% CI, 12.6-18.8], respectively). Although the trial was not powered to compare efficacy between treatment groups by different chemotherapy regimens, the increase in OS was observed for KEYTRUDA plus chemotherapy across the three chemotherapy choices. These data were presented in an oral presentation at the European Society for Medical Oncology (ESMO) Congress 2021 (Abstract #LBA16). There was no statistically significant difference in OS between the treatment groups in the CPS =1 population; due to statistical testing hierarchy, formal testing was not performed in the intention-to-treat (ITT) population. The incidence of treatment-related adverse events (TRAEs) was similar among patients in the two treatment groups, with Grade 3-5 TRAEs occurring in 68.1% of patients in the KEYTRUDA plus chemotherapy arm and 66.9% of patients in the chemotherapy arm. Treatment-related adverse events led to discontinuation in 18.3% of patients in the KEYTRUDA plus chemotherapy arm and 11.0% of patients in the chemotherapy arm. These OS data follow prior analyses from KEYNOTE-355 that showed KEYTRUDA plus chemotherapy resulted in a statistically significant and clinically meaningful improvement in progression-free survival (PFS) compared with chemotherapy alone for the first-line treatment of patients with mTNBC whose tumors expressed PD-L1 (CPS =10) and supported approval of this regimen in the U.S. and Japan. In the U.S., KEYTRUDA was granted accelerated approval by the U.S. Food and Drug Administration in November 2020 and was subsequently granted regular approval in July 2021. In Europe, the Committee for Medicinal Products for Human Use of the European Medicines Agency recently adopted a positive opinion recommending approval of KEYTRUDA in combination with chemotherapy for this patient population. Merck is rapidly advancing a broad portfolio in gynecologic and breast cancers through an extensive clinical development program for KEYTRUDA and several other investigational and approved medicines across these areas.