In arm B, pembrolizumab will be started and SBRT given before the 2nd course of pembrolizumab to the 1-3 most clinically significant lesions. After SBRT, untreated measurable disease must remain to assess the activity of pembrolizumab. The value of a treatment strategy that combines pembrolizumab and SBRT up-front is evaluated in this arm. Giving SBRT early to the most clinically significant cancer lesions may give pembrolizumab more time to work and may improve response by generating neo-antigens.