Pembrolizumab and Cabozantinib in Recurrent and/or Metastatic Head and Neck Squamous Cell Carcinoma: Long-term Survival Update with a Biomarker Analysis.

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Anti-programmed cell death protein 1 (PD-1) therapy is a standard of care in recurrent and/or metastatic head and neck squamous cell carcinoma (RMHNSCC). Vascular endothelial growth factor receptor tyrosine kinase inhibitors (VEGFR-TKI) have immunomodulatory properties and improve clinical outcomes in combination with anti-PD-1 therapy in different malignancies. We report the long-term efficacy and safety of pembrolizumab and cabozantinib in patients with RMHNSCC and include a correlative biomarker analysis. This open-label, single-arm, multicenter, phase 2 study screened 50 patients with RMHNSCC, of whom 36 received pembrolizumab and cabozantinib. The primary endpoint was overall response rate (ORR), safety, and tolerability. Secondary endpoints included progression-free survival (PFS), overall survival (OS), and correlative studies of tissue and blood. We report the long-term PFS, OS, and safety of treated patients and describe correlative biomarkers evaluating p-MET expression and tumor immune microenvironment (TIME) using multiplex immunohistochemistry. With median follow-up of 22.4 months, the median PFS was 12.8 months with a 2-year PFS of 32.6% (95% CI, 18.8%-56.3%) and the median OS was 27.7 months with a 2-year OS of 54.7% [95% confidence interval (CI), 38.9%-76.8%]. The median duration of response was 12.6 months with a 2-year rate of 38.5% (95% CI, 30.8%-81.8%). Long-term treatment-related adverse events included manageable hypothyroidism (5.5%) and grade 1 elevated aspartate aminotransferase and alanine aminotransferase (2.8%). Baseline tumor p-MET expression correlated with ORR (P = 0.0055). Higher density of CD8+, CD103+, and CSF1-R+ cells at baseline correlated with improved OS [hazard ratio (HR) = 5.27, P = 0.030; HR = 8.79, P = 0.017; HR = 6.87, P = 0.040, respectively]. Pembrolizumab and cabozantinib provided prolonged encouraging long-term disease control and survival with a maintained favorable safety profile. The prognostic significance of higher density of CD8+, CD103+, and CSF1-R+ cells in TIME deserve further evaluation in similar clinical settings.