Pembrolizumab +/- SD-101 in Hormone-Naïve Oligometastatic Prostate Cancer With RT and iADT

200 mg IV every 21 days for up to 13 doses (Arms 1 and 2)

5 mg will be delivered to the dominant prostatic tumor lesion at time of fiducial marker placement (1-5 weeks prior to Cycle 1, Day 1) and and 1-3 weeks after Cycle 1 Day 1

22.5 mg will be given intramuscularly (IM). First injection 3 months prior to Cycle 1 Day 1. Intermittent androgen deprivation therapy will be given every 3 months starting Cycle 1, Day 1 for 3 additional doses.

1000 mg oral dosage will be given daily for 3 months prior to Cycle 1, Day 1 and daily for 9 months starting Cycle 1, Day 1.

5 mg oral dosage will be given daily for 3 months prior to Cycle 1 Day 1 and daily for 9 months starting Cycle 1, Day 1.

7 Gy x 5 fractions (35 Gy total) 1-2 weeks after fiducial marker placement and simulation over 10-14 days.