Merck & Co. announced detailed results from the KEYNOTE-522 study, with the Keytruda (pembrolizumab) regimen reducing the risk of event-free survival (EFS) events by 37% versus the chemotherapy-placebo regimen in patients with high-risk, early-stage triple-negative breast cancer (TNBC). The company noted that "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."
In May, the company reported that the KEYNOTE-522 trial met its second co-primary endpoint of EFS, having previously hit its other main goal of pathological complete response (pCR). The study evaluated neoadjuvant Keytruda in combination with chemotherapy followed by Keytruda monotherapy compared with neoadjuvant chemotherapy followed by adjuvant placebo in 1174 patients with high-risk early-stage TNBC.
Results showed that 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 those given the chemotherapy-placebo regimen. Merck indicated that in pre-specified exploratory subgroup analyses, the EFS benefit seen with the Keytruda regimen was independent of PD-L1 expression. In the PD-L1-positive subgroup, the Keytruda regimen reduced the risk of EFS events by 33% versus the chemotherapy-placebo regimen, while in the PD-L1-negative subgroup, the Keytruda regimen cut the risk of EFS events by 52%.
Merck added that although overall survival data have not crossed the boundary for statistical significance after a median follow-up of 39 months, there was a 28% reduction in the risk of death with the Keytruda regimen versus the chemotherapy-placebo regimen. The drugmaker noted that the trial will continue to allow for additional follow-up of OS, which is a key secondary endpoint.
Last year, Keytruda was granted accelerated approval in the US in combination with chemotherapy for the treatment of patients with locally recurrent unresectable or metastatic TNBC whose tumours express PD-L1. Earlier data from the KEYNOTE-522 trial were used by Merck to file for expanded approval to include patients with high-risk, early-stage TNBC, although the FDA issued a complete response letter, calling for further EFS data from the study. The company noted that the latest findings, which were presented at a European Society for Medical Oncology (ESMO) virtual plenary, have been submitted to the FDA.
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