Inclusion Criteria:  Histological diagnosis of primary RCC Histological or radiographic diagnosis of metastatic RCC Age >= 18 years Eastern Cooperative Oncology Group (ECOG) performance status 0-3 Feasible vascular access as determined by study staff Undergoing standard of care SBRT or PCA to RCC metastatic lesion(s) Provide written informed consent Willing to consent to research blood draws Willing to return to enrolling institution for follow-up  Exclusion Criteria:  Prior local treatment of the index metastatic lesion Pregnant or nursing women Co-morbid systemic illnesses or other severe concurrent disease which, in the judgment of the investigator, would make the patient inappropriate for study entry