Pembrolizumab is a humanized antibody used in cancer immunotherapy for various types of cancers. However, the activity of pembrolizumab in the CNS has not been documented. This study aims to investigate the activity of pembrolizumab in patients with non-small-cell lung cancer (NSCLC) or melanoma with untreated brain metastases.

This phase 2, open-label study included a total of 42 patients aged 18 years or more with stage IV NSCLC with at least one brain metastasis 5–20 mm in size. The patients were divided into two cohorts: cohort A with PD-L1 expression of at least 1% and cohort B with PD-L1 less than 1% or unevaluable. The patients were assigned to receive pembrolizumab 10 mg/kg intravenously every 2 weeks. The primary outcome of the study was the brain metastasis response.

During a median follow-up of 8.3 months, 37 patients in cohort A had a brain metastasis response, compared to no response in cohort B. Commonly occurring grade 3 or 4 adverse events included pneumonitis, colitis, adrenal insufficiency, hypokalemia, hyperglycemia. The incidence rate of treatment-related adverse events was 14%, though no treatment-related deaths were reported.

The research concluded that pembrolizumab exhibited activity in patients with brain metastases and NSCLC with PD-L1 expression of at least 1%.