Merck’s KEYTRUDA® (pembrolizumab) in Combination with Chemotherapy Met Primary Endpoint of Progression-Free Survival (PFS) as First-Line Treatment for Metastatic Triple-Negative Breast Cancer (mTNBC)

In Clinical Studies News by Barbara Jacoby


In Pivotal Phase 3 KEYNOTE-355 Study, KEYTRUDA Plus Chemotherapy Significantly Improved PFS Compared to Chemotherapy Alone in Patients with mTNBC Whose Tumors Expressed PD-L1 (CPS ≥10)

Data to be Presented at an Upcoming Medical Congress and Discussed with Regulatory Authorities

Merck (NYSE: MRK), known as MSD outside the United States and Canada, today announced that the pivotal Phase 3 KEYNOTE-355 trial investigating KEYTRUDA, Merck’s anti-PD-1 therapy, in combination with chemotherapy met one of its dual primary endpoints of progression-free survival (PFS) in patients with metastatic triple-negative breast cancer (mTNBC) whose tumors expressed PD-L1 (Combined Positive Score [CPS] ≥10). Based on an interim analysis conducted by an independent Data Monitoring Committee (DMC), first-line treatment with KEYTRUDA in combination with chemotherapy (nab-paclitaxel, paclitaxel or gemcitabine/carboplatin) demonstrated a statistically significant and clinically meaningful improvement in PFS compared to chemotherapy alone in these patients. Based on the recommendation of the DMC, the trial will continue without changes to evaluate the other dual primary endpoint of overall survival (OS). The safety profile of KEYTRUDA in this trial was consistent with that observed in previously reported studies; no new safety signals were identified.

“Triple-negative breast cancer is an aggressive malignancy. It is very encouraging that KEYTRUDA in combination with chemotherapy has now demonstrated positive results as both a first-line treatment in the metastatic setting with this trial, and as neoadjuvant therapy in the KEYNOTE-522 trial,” said Dr. Roger M. Perlmutter, president, Merck Research Laboratories. “We look forward to sharing these findings with the medical community at an upcoming congress and discussing them with the FDA and other regulatory authorities.”

The KEYTRUDA breast cancer clinical development program encompasses several internal and external collaborative studies. In addition to KEYNOTE-355, in TNBC these include the ongoing registration-enabling studies KEYNOTE-242 and KEYNOTE-522.

About KEYNOTE-355

KEYNOTE-355 is a randomized, two-part, Phase 3 trial (, NCT02819518) evaluating KEYTRUDA in combination with one of three different chemotherapies (investigator’s choice of either nab-paclitaxel, paclitaxel or gemcitabine/carboplatin) compared with placebo plus one of the three chemotherapy regimens for the treatment of locally recurrent inoperable or mTNBC that has not been previously treated with chemotherapy in the metastatic setting. Part 1 of the study was open-label and evaluated the safety and tolerability of KEYTRUDA in combination with either nab-paclitaxel, paclitaxel or gemcitabine/carboplatin in 30 patients. Part 2 of KEYNOTE-355 was double-blinded, with dual primary endpoints of OS and PFS in all participants and in participants whose tumors expressed PD-L1 (CPS ≥1 and CPS ≥10). The secondary endpoints include objective response rate (ORR), duration of response (DOR), disease control rate (DCR) and safety.

Part 2 of KEYNOTE-355 enrolled 847 patients who were randomized to receive KEYTRUDA (200 mg intravenously [IV] on day 1 of each 21-day cycle) plus nab-paclitaxel (100 mg/m2 IV on days 1, 8 and 15 of each 28-day cycle), paclitaxel (90 mg/m2 IV on days 1, 8 and 15 of each 28-day cycle) or gemcitabine/carboplatin (1,000 mg/m2 [gemcitabine] and Area Under the Curve [AUC] 2 [carboplatin] on days 1 and 8 of each 21-day cycle); or placebo (normal saline on day 1 of each 21-day cycle) plus nab-paclitaxel (100 mg/m2 IV on days 1, 8 and 15 of each 28-day cycle), paclitaxel (90 mg/m2 IV on days 1, 8 and 15 of each 28-day cycle) or gemcitabine/carboplatin (1,000 mg/m2 [gemcitabine] and AUC 2 [carboplatin] on days 1 and 8 of each 21-day cycle).

About Triple-Negative Breast Cancer (TNBC)

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 estrogen 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 15-20% of patients with breast cancer are diagnosed with TNBC.

About KEYTRUDA® (pembrolizumab) Injection, 100 mg

KEYTRUDA is an anti-PD-1 therapy that works by increasing the ability of the body’s immune system to help detect and fight tumor cells. KEYTRUDA is a humanized monoclonal antibody that blocks the interaction between PD-1 and its ligands, PD-L1 and PD-L2, thereby activating T lymphocytes which may affect both tumor cells and healthy cells.

Merck has the industry’s largest immuno-oncology clinical research program. There are currently more than 1,000 trials studying KEYTRUDA across a wide variety of cancers and treatment settings. The KEYTRUDA clinical program seeks to understand the role of KEYTRUDA across cancers and the factors that may predict a patient’s likelihood of benefitting from treatment with KEYTRUDA, including exploring several different biomarkers.