KEYNOTE-522 Is the First Phase 3 Study With an Immunotherapy to Show Positive EFS Results in High-Risk Early-Stage Triple-Negative Breast Cancer

Merck Has Submitted These Data From KEYNOTE-522 to the US FDA for Review

KENILWORTH, N.J.--(BUSINESS WIRE)-- Merck (NYSE: MRK), known as MSD outside the United States and Canada, today announced positive event-free survival (EFS) data from the pivotal neoadjuvant/adjuvant Phase 3 study KEYNOTE-522. The trial investigated neoadjuvant KEYTRUDA, Merck’s anti-PD-1 therapy, plus chemotherapy followed by adjuvant KEYTRUDA as monotherapy (the KEYTRUDA regimen) compared with neoadjuvant chemotherapy followed by adjuvant placebo (the chemotherapy-placebo regimen) in patients with high-risk early-stage triple-negative breast cancer (TNBC). This is the first time an anti-PD-1/L1 therapy has demonstrated a statistically significant EFS result as combined neoadjuvant and adjuvant therapy for these patients. These results are being presented today during a European Society for Medical Oncology (ESMO) Virtual Plenary.

After a median follow-up of 39 months, the KEYTRUDA regimen reduced the risk of EFS events by 37% (HR=0.63 [95% CI, 0.48-0.82]; p=0.00031) versus the chemotherapy-placebo regimen – a statistically significant and clinically meaningful EFS result. EFS was defined as the time from randomization to the first occurrence of either disease progression that precluded definitive surgery, a local/distant recurrence, a second primary cancer, or death from any cause. As previously announced, KEYNOTE-522 met the dual primary endpoint of pathological complete response (pCR) at the first interim analysis. The trial is continuing to allow for additional follow-up of overall survival (OS), a key secondary endpoint. At this fourth interim analysis, although these data have not crossed the boundary for statistical significance, there was a 28% reduction in the risk of death with the KEYTRUDA regimen versus the chemotherapy-placebo regimen (HR=0.72 [95% CI, 0.51-1.02]; p=0.03214). The safety profile of the KEYTRUDA regimen was consistent with the known profiles of each regimen, and no new safety concerns were identified.

“Given the high rates of recurrence within the first five years of diagnosis, patients with high-risk early-stage TNBC need new treatment options,” said Dr. Peter Schmid, lead, Centre for Experimental Cancer Medicine, Barts Cancer Institute in London, England. “KEYNOTE-522 was designed to study whether the combined neoadjuvant and adjuvant regimen with KEYTRUDA could help treat the cancer earlier. Now, with more than three years of follow-up, we see the potential of this approach. These event-free survival data are very encouraging for patients and show that this combination of KEYTRUDA plus chemotherapy as neoadjuvant therapy, followed by single-agent KEYTRUDA as adjuvant therapy, may offer women with high-risk early-stage TNBC a new treatment option for this aggressive disease.”

“These highly anticipated event-free survival results in this TNBC population build upon earlier findings from the KEYNOTE-522 trial and further support the potential use of KEYTRUDA in these patients,” said Dr. Vicki Goodman, vice president, clinical research, Merck Research Laboratories. “KEYNOTE-522 is the first large randomized Phase 3 study to report a statistically significant and clinically meaningful EFS result among patients with stage II and stage III TNBC. We have submitted these data to the FDA and are working closely with the agency on its review of our application.”

KEYTRUDA is currently approved under accelerated approval in the U.S. 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.

Merck is rapidly advancing a broad portfolio in women’s cancers with an extensive clinical development program for KEYTRUDA and several other investigational and approved medicines across multiple gynecologic and breast cancers. The KEYTRUDA clinical development program for TNBC encompasses several internal studies and external collaborative trials, including the ongoing studies KEYNOTE-242 and KEYNOTE-355.

Study Design and Additional Data From KEYNOTE-522

KEYNOTE-522 is a Phase 3, randomized, double-blind trial (ClinicalTrials.gov, NCT03036488). The dual primary endpoints are pCR, defined as pathological stage ypT0/Tis ypN0 at the time of definitive surgery, and EFS, defined as the time from randomization to the first occurrence of either disease progression that precluded definitive surgery, a local/distant recurrence, a second primary cancer, or death from any cause in all patients randomized. Secondary endpoints include pCR rate using alternative definitions, OS in all patients randomized, pCR rate according to all definitions, EFS and OS in patients whose tumors express PD-L1 (CPS ≥1), safety and health-related quality of life assessments. The study enrolled 1,174 patients who were randomized 2:1 to receive either:

• The KEYTRUDA regimen: KEYTRUDA (every three weeks) plus paclitaxel (weekly) and carboplatin (weekly or every three weeks) for four cycles, followed by KEYTRUDA plus cyclophosphamide and either doxorubicin or epirubicin (every three weeks) for four cycles as neoadjuvant therapy prior to surgery, followed by nine cycles of KEYTRUDA (every three weeks) as adjuvant therapy post-surgery (n=784)
• The chemotherapy-placebo regimen: Placebo (every three weeks) plus paclitaxel (weekly) and carboplatin (weekly or every three weeks) for four cycles, followed by placebo plus cyclophosphamide and either doxorubicin or epirubicin (every three weeks) for four cycles as neoadjuvant therapy prior to surgery, followed by nine cycles of placebo (every three weeks) as adjuvant therapy post-surgery (n=390)

As previously announced, KEYNOTE-522 met the success criterion for the dual primary endpoint of pCR at the first interim analysis; pCR was observed in 64.8% of patients treated with KEYTRUDA plus chemotherapy (n=401), an increase of 13.6% (p=0.00055) from 51.2% in patients treated with placebo plus chemotherapy (n=201). At the fourth interim analysis, KEYNOTE-522 met the success criterion for the dual primary endpoint of EFS. The study is continuing to allow for additional follow-up of OS.

At three years, 84.5% of patients treated with the KEYTRUDA regimen were alive and did not experience an EFS event compared to 76.8% of patients treated with the chemotherapy-placebo regimen.

In pre-specified exploratory subgroup analyses of EFS, the EFS benefit seen with the KEYTRUDA regimen was independent of PD-L1 expression. In the PD-L1-positive subgroup (n=973), defined as CPS ≥1, treatment with the KEYTRUDA regimen reduced the risk of EFS events by 33% (HR=0.67 [95% CI, 0.49-0.92]) versus the chemotherapy-placebo regimen. In the PD-L1-negative subgroup (n=197), defined as CPS