On May 31, 2025 Merck (NYSE: MRK), known as MSD outside of the United States and Canada, reported that KEYTRUDA (pembrolizumab) plus Trodelvy (sacituzumab govitecan-hziy) reduced the risk of disease progression or death by 35% (HR=0.65, p<0.001) versus KEYTRUDA plus chemotherapy for the first-line treatment of patients with PD-L1+ (Combined Positive Score [CPS] ≥10) inoperable (unresectable) locally advanced or metastatic triple-negative breast cancer (TNBC), as determined by an FDA-approved test. KEYTRUDA, when given in combination with Gilead’s TROP2 antibody-drug conjugate (ADC) Trodelvy, resulted in a median progression-free survival (PFS) of 11.2 months versus 7.8 months when KEYTRUDA was given in combination with chemotherapy (Press release, Merck & Co, MAY 31, 2025, View Source [SID1234653548]). These data from the pivotal Phase 3 ASCENT-04/KEYNOTE-D19 study will be presented today as a late-breaking oral presentation at the 2025 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Annual Meeting (Abstract #LBA109) and were selected for the official ASCO (Free ASCO Whitepaper) Press Program.
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"These results have the potential to be an important advancement for patients with PD-L1–positive metastatic triple-negative breast cancer, a population for whom first-line options remain limited," said Sara Tolaney, MD, MPH, Dana-Farber Cancer Institute and primary investigator of the ASCENT-04/KEYNOTE-D19 study. "By combining sacituzumab govitecan with pembrolizumab, we’re seeing meaningful gains in progression-free survival and a promising trend in overall survival—findings that could support a new frontline standard of care for this aggressive disease."
The safety profile of KEYTRUDA plus Trodelvy in this study was consistent with the known safety profile of each agent. No new safety signals were identified with the combination. The two companies plan to share these results with regulatory authorities worldwide.
"We’re committed to building on the established role of KEYTRUDA as a foundational treatment for people with TNBC to provide new options in earlier lines of treatment, in the hope of improving outcomes for people living with this disease," said Dr. Marjorie Green, senior vice president and head of oncology, global clinical development, Merck Research Laboratories. "These data support the addition of this TROP2-directed ADC to KEYTRUDA, demonstrating the potential to help people with TNBC and to give doctors another option to treat this disease."
A statistically significant and clinically meaningful improvement was observed with KEYTRUDA plus Trodelvy (n=221), showing a 35% reduction in the risk of disease progression or death (HR=0.65; p<0.001) in the intent-to-treat population compared to KEYTRUDA plus chemotherapy (n=222). The PFS benefit was generally consistent across key prespecified subgroups including age, curative treatment-free interval and geographic region.
A higher objective response rate (ORR) was observed for the KEYTRUDA plus Trodelvy combination (59.7% [95% CI, 52.9-66.3] versus 53.2% [95% CI, 46.4-59.9]), including 13% and 8% with a complete response, respectively, in the KEYTRUDA plus Trodelvy and KEYTRUDA plus chemotherapy arms. Notably, a substantially longer duration of response (DOR) was observed with KEYTRUDA plus Trodelvy (16.5 months [95% CI, 12.7-19.5] versus 9.2 months [95% CI, 7.6-11.3]). Encouraging trends in overall survival (OS) were also observed, but data are immature at the time of PFS primary analysis. Overall survival follow-up remains ongoing and will continue to be monitored as a key secondary endpoint.
Merck has a comprehensive clinical development program in various subtypes of breast cancer including evaluating KEYTRUDA in combination with investigational TROP2 ADCs (trophoblast cell-surface antigen-directed antibody-drug conjugates) in metastatic and early-stage cancers. The company has four ongoing Phase 3 studies in breast cancer, with two being in metastatic disease.
In the U.S. and Europe, KEYTRUDA has two approved indications in TNBC: for the treatment of patients with high-risk early-stage TNBC in combination with chemotherapy as neoadjuvant treatment, and then continued as a single agent as adjuvant treatment after surgery; and in combination with chemotherapy for the treatment of patients with locally recurrent unresectable or metastatic TNBC whose tumors express PD-L1 (CPS ≥10) as determined by an FDA-approved test.
As announced, data spanning more than 25 types of cancer are being presented from Merck’s broad oncology portfolio and investigational pipeline at the 2025 ASCO (Free ASCO Whitepaper) Annual Meeting.
About the ASCENT-04/KEYNOTE-D19 Study
In 2021, Merck entered a collaboration with Gilead to investigate KEYTRUDA plus Trodelvy in the Phase 3 ASCENT-04/KEYNOTE-D19 open-label, global trial (ClinicalTrials.gov, NCT05382286). The primary endpoint is PFS as determined by BICR using RECIST v1.1. Secondary endpoints include OS, ORR, DOR, time to onset of response (TTR), patient-reported outcomes (PROs) and safety. The study enrolled 443 patients who were randomized in a 1:1 ratio to receive either sacituzumab govitecan (10 mg/kg intravenously [IV] on Days 1 and 8 of a 21-day cycle) plus pembrolizumab (200 mg IV on Day 1 of a 21-day cycle) or chemotherapy plus pembrolizumab. The chemotherapy regimen included gemcitabine plus carboplatin, paclitaxel, or nab-paclitaxel. Treatment continued until blinded independent central review (BICR)-verified disease progression or unacceptable toxicity and at this time patients randomized to chemotherapy were allowed to crossover and receive sacituzumab govitecan upon disease progression.
About triple-negative breast cancer (TNBC)
Triple-negative breast cancer is the most aggressive type of breast cancer, which has the highest risk of recurrence within the first five years after diagnosis and is associated with worse outcomes compared to other forms of breast cancer. Approximately 10-15% of patients with breast cancer are diagnosed with TNBC. While some breast cancers may test positive for estrogen receptors, progesterone receptors or overexpression of human epidermal growth factor receptor 2 (HER2), TNBC tests negative for all three. Triple-negative breast cancer tends to be more common in people who are younger than 40 years of age, who are Black or who have a BRCA1 mutation.