RecruitingPhase 1Drug trialA Study of Pembrolizumab and Ablation (Cryoablation or Histotripsy) in People With Breast CancerParticipants will have a confirmed diagnosis of metastatic breast cancer and will receive pembrolizumab in combination with ablation (cryoablation or histotripsy) OR pembrolizumab alone. Participants will be randomly assigned.