Officials with the FDA have approved pembrolizumab (Keytruda; Merck), an anti-PD-1 therapy, in combination with chemotherapy for the treatment of patients with locally recurrent unresectable or metastatic triple-negative breast cancer (TNBC) whose tumors express PD-L1 (Combined Positive Score [CPS] ≥10) as determined by an FDA-approved test.
Pembrolizumab was previously granted approvals for treatment of certain patients with various types of cancers including melanoma, lung cancers, head and neck squamous cell cancer, lymphomas, and more. However, the newest indication is the first approval of pembrolizumab for breast cancer, according to Merck.
TNBC is an aggressive type of breast cancer that characteristically has a high recurrence rate within the first 5 years after diagnosis. Approximately 15%-20% of patients with breast cancer are diagnosed with TNBC, according to Merck. The FDA’s decision to approve pembrolizumab for treating patients with TNBC whose tumors express PD-L1 is an accelerated approval.
The FDA’s approval is based on results from the Phase 3 KEYNOTE-355 (NCT02819518) trial, where pembrolizumab in combination with chemotherapy—paclitaxel (pac), paclitaxel protein-bound (nab-paclitaxel), or gemcitabine (gem) and carboplatin (carbo)—was shown to significantly reduce the risk of disease progression or death by 35% for patients whose tumors express PD-L1 versus the same chemotherapy regimens alone (HR=0.65 [95% CI, 0.49, 0.86]; p=0.0012). Events were observed in 62% of 220 patients receiving pembrolizumab in combination with pac, nab-paclitaxel or gem/carbo versus 77% of 103 patients with the same chemotherapy regimens alone. In the trial, 38% of patients had tumors expressing PD-L1 with CPS ≥10.
During the trial, fatal adverse events occurred in 2.5% of patients, including cardio-respiratory arrest (0.7%) and septic shock (0.3%). Serious adverse reactions occurred in 30% of patients receiving pembrolizumab in combination with chemotherapy, of which the most common were pneumonia (2.9%), anemia (2.2%), and thrombocytopenia (2%). Pembrolizumab was discontinued in 11% of patients due to adverse reactions.
The most common adverse reactions resulting in permanent discontinuation (≥1%) were increased ALT (2.2%), increased AST (1.5%), and pneumonitis (1.2%). The most common adverse reactions (≥20%) in patients receiving pembrolizumab in combination with chemotherapy were: fatigue (48%), nausea (44%), alopecia (34%), diarrhea and constipation (28% each), vomiting and rash (26% each), cough (23%), decreased appetite (21%), and headache (20%).