On July 28, 2023 Merck (NYSE: MRK), known as MSD outside of the United States and Canada, reported that the pivotal Phase 3 KEYNOTE-756 trial investigating KEYTRUDA, Merck’s anti-PD-1 therapy, in combination with chemotherapy met one of its dual primary endpoints of pathological complete response (pCR) rate following the neoadjuvant part of the neoadjuvant/adjuvant study regimen in patients with high-risk, early-stage estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) breast cancer (Press release, Merck & Co, JUL 28, 2023, View Source;Breast-Cancer/?feedref=JjAwJuNHiystnCoBq_hl-SZsvSFSeS2k6e-jDETKtk7rEQumBjqILHhqiwHg7GoJnkvYMqDDYxFrLs-oQ2BHQ-mJCMFkCosC_NGzuJ8TW18j0KvNpL5ik-rnXyj1_o5vU-QF2vCj0ELWlPt_oGwViA== [SID1234633482]). At a prespecified interim analysis conducted by an independent Data Monitoring Committee (DMC), the KEYTRUDA-based regimen demonstrated a statistically significant improvement in pCR rate compared to neoadjuvant placebo plus chemotherapy. A pCR is defined as a lack of all signs of cancer in tissue samples analyzed following completion of neoadjuvant therapy and definitive surgery.

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Based on the recommendation of the DMC, the trial will continue without changes to evaluate the other dual primary endpoint of event-free survival (EFS), per the trial design. The safety profile of KEYTRUDA in this trial was consistent with that observed in previously reported studies; no new safety signals were identified. Results will be presented at an upcoming medical meeting.

"This is the first positive Phase 3 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," said Dr. Gursel Aktan, vice president, global clinical development, Merck Research Laboratories. "We look forward to sharing the detailed results with the medical community and thank the patients and investigators for their important contributions to this study."

"While significant advancements have been made in the treatment of ER-positive, HER2-negative breast cancer, people diagnosed with high-risk disease as assessed by clinical and pathologic criteria typically have a worse prognosis and limited options before surgery," said Dr. Fatima Cardoso, director of the Breast Unit of the Champalimaud Clinical Centre, Lisbon, Portugal and co-principal investigator. "Data from KEYNOTE-756 suggest that adding pembrolizumab to neoadjuvant chemotherapy before surgery can significantly improve the pCR rate compared to neoadjuvant chemotherapy alone for people with high-risk, early-stage ER-positive, HER2-negative breast cancer."

"Worldwide, more than two million people are diagnosed with breast cancer each year, and it is critically important that breast cancer is found and treated early, especially for patients with high-risk disease," said Dr. Aditya Bardia, attending physician, medical oncology, Massachusetts General Hospital, director, breast cancer research, Massachusetts General Cancer Center, Associate professor, Harvard Medical School and co-principal investigator. "While we wait for event-free survival data, these initial pCR results provide a potentially encouraging signal and may have important therapeutic implications for patients with high-risk, early-stage ER-positive, HER2-negative breast cancer."

In the U.S., KEYTRUDA is approved for two indications for the treatment of patients with triple-negative breast cancer (TNBC). Based on results from KEYNOTE-522, KEYTRUDA is approved in combination with chemotherapy as neoadjuvant treatment, and then continued as a single agent as adjuvant treatment after surgery for patients with high-risk, early-stage TNBC. Based on results from KEYNOTE-355, KEYTRUDA is approved in combination with chemotherapy for the treatment of patients with locally recurrent unresectable or metastatic TNBC whose tumors express PD-L1 (combined positive score [CPS ≥10]) as determined by an FDA-approved test. In addition to the U.S., KEYNOTE-522 and KEYNOTE-355 supported the approvals of KEYTRUDA-based regimens for certain patients with high-risk early-stage TNBC and locally recurrent unresectable metastatic TNBC, respectively, in more than 90 countries around the world.

About KEYNOTE-756

KEYNOTE-756 is a randomized, double-blind Phase 3 trial (ClinicalTrials.gov, NCT03725059) evaluating KEYTRUDA in combination with chemotherapy as neoadjuvant treatment, followed by adjuvant treatment with KEYTRUDA plus endocrine therapy for the treatment of high-risk, early-stage ER+/HER2- breast cancer. The dual primary endpoints are pCR rate and EFS, and secondary endpoints include overall survival and safety. The trial enrolled 1,240 patients who were randomized 1:1 to receive:

KEYTRUDA (200 mg every three weeks [Q3W]) plus chemotherapy (paclitaxel weekly) for four cycles, followed by four additional cycles of KEYTRUDA in combination with chemotherapy (doxorubicin or epirubicin plus cyclophosphamide) as neoadjuvant therapy prior to surgery, followed by nine cycles of KEYTRUDA (Q3W) plus endocrine therapy (for up to 10 years) as adjuvant therapy post-surgery; or,
Placebo (Q3W) plus chemotherapy (paclitaxel weekly) for four cycles, followed by four additional cycles of placebo in combination with chemotherapy (doxorubicin or epirubicin plus cyclophosphamide) as neoadjuvant therapy prior to surgery, followed by nine cycles of placebo (Q3W) plus endocrine therapy (for up to 10 years) as adjuvant therapy post-surgery.
About breast cancer

Breast cancer is one of the leading causes of cancer-related death in women worldwide, with more than two million patients diagnosed and approximately 685,000 deaths from the disease globally in 2020. In the U.S., it is estimated there will be approximately 298,000 patients diagnosed with breast cancer and 43,700 deaths from the disease in 2023. The are many different types of breast cancer and various subtypes. Of all breast cancer patients, about 70% will be diagnosed with hormone receptor-positive, HER2-negative disease. Cancer recurrence following surgery for this type of cancer is most common within five years, and patients with high-risk features have a greater chance of recurrence.