PDCD1 and head and neck squamous cell carcinoma: Differences between the designs of these two studies include the anti-PD-1 agent used (nivolumab vs pembrolizumab), the type of cancer (HNSCC vs NSCLC), timing of SBRT (between first and second dose of nivolumab vs prior to starting pembrolizumab), and dose of SBRT (9 Gy ×3 fractions vs 8 Gy ×3 fractions).