External beam photon stereotactic body radiotherapy (SBRT) using a linear accelerator to a total dose of 40 Gy in 5 fractions delivered once daily with at least 48 hours between each fraction. SBRT treatment will be completed within a 21-day window. Starting within 14 days after completion of SBRT, intravenous nivolumab 240 mg will be given every 2 weeks as monotherapy or in combination with ipilimumab 1 mg/kg IV every 6 weeks.