Pembrolizumab in brain metastases of diverse histologies: phase 2 trial results.

Brain metastases (BMs) are an emerging challenge in oncology due to increasing incidence and limited treatments. Here, we present results of a single-arm, open-label, phase 2 trial evaluating intracranial efficacy of pembrolizumab, a programmed cell death protein 1 inhibitor, in 9 patients with untreated BMs (cohort A) and 48 patients with recurrent and progressive BMs (cohort B) across different histologies. The primary endpoint was the proportion of patients achieving intracranial benefit, defined by complete response, partial response or stable disease. The primary endpoint was met with an intracranial benefit rate of 42.1% (90% confidence interval (CI): 31-54%). The median overall survival, a secondary endpoint, was 8.0 months (90% CI: 5.5-8.7 months) across both cohorts, 6.5 months (90% CI: 4.5-18.7 months) for cohort A and 8.1 months (90% CI: 5.3-9.6 months) for cohort B. Seven patients (12.3%), encompassing breast, melanoma and sarcoma histologies, had overall survival greater than 2 years. Thirty patients (52%; 90% CI: 41-64%) had one or more grade-3 or higher adverse events that were at least possibly treatment related. Two patients had grade-4 adverse events (cerebral edema) that were deemed at least possibly treatment related. These results suggest that programmed cell death protein 1 blockade may benefit a select group of patients with BMs, and support further studies to identify biomarkers and mechanisms of resistance. ClinicalTrials.gov identifier: NCT02886585.

Microenvironmental Landscape of Human Melanoma Brain Metastases in Response to Immune Checkpoint Inhibition.

Melanoma-derived brain metastases (MBM) represent an unmet clinical need because central nervous system progression is frequently an end stage of the disease. Immune checkpoint inhibitors (ICI) provide a clinical opportunity against MBM; however, the MBM tumor microenvironment (TME) has not been fully elucidated in the context of ICI. To dissect unique elements of the MBM TME and correlates of MBM response to ICI, we collected 32 fresh MBM and performed single-cell RNA sequencing of the MBM TME and T-cell receptor clonotyping on T cells from MBM and matched blood and extracranial lesions. We observed myeloid phenotypic heterogeneity in the MBM TME, most notably multiple distinct neutrophil states, including an IL8-expressing population that correlated with malignant cell epithelial-to-mesenchymal transition. In addition, we observed significant relationships between intracranial T-cell phenotypes and the distribution of T-cell clonotypes intracranially and peripherally. We found that the phenotype, clonotype, and overall number of MBM-infiltrating T cells were associated with response to ICI, suggesting that ICI-responsive MBMs interact with peripheral blood in a manner similar to extracranial lesions. These data identify unique features of the MBM TME that may represent potential targets to improve clinical outcomes for patients with MBM.