Phase II trial of Keytruda (pembrolizumab) shows drug shrank tumours by 30 per cent in patients with metastatic triple negative breast cancer- Merck Inc

The immunotherapy drug Keytruda (pembrolizumab), from Merck Inc, has been found to be effective in patients with metastatic triple negative breast cancer, according to an international phase II clinical trial. The trial investigated the drug in two separate cohorts of patients: Cohort A, which included 170 patients with heavily pretreated metastatic triple negative breast cancer (mTNBC) regardless of PD-L1 expression, and Cohort B, which included 52 patients with PD-L1-positive tumors who received it as first-line therapy.

In Cohort A, pembrolizumab shrunk tumors by more than 30 percent in eight of 170 patients, or five percent, and stabilized the disease in 35, or 21 percent, of those previously treated for mTNBC. Of the eight who experienced tumor reduction, all of them lived at least another year. The remaining patients in this cohort had a lower chance of survival. In Cohort B—those who received pembrolizumab as first-line therapy—12 of 52 patients, or 23 percent, saw tumors shrink by more than 30 percent, while the disease was stabilized in nine of them, or 17 percent.

This multi-site trial was conducted at 17 medical centers across four continents. Cohort A is the first phase II study of an immunotherapy for triple negative breast cancer to be reported and represents the largest cohort of patients with mTNBC treated with immunotherapy to date. The goals of Cohort B, for which survival data are not yet complete, were, primarily, to prove pembrolizumab's safety and, secondarily, to explore its efficacy as a first-line treatment. Both goals appear to have been met. Data were presented at the annual meeting of the American Society of Clinical Oncology.