• Locally advanced unresectable or metastatic RCC with either a component of clear cell histology or carbonic anhydrase-IX (CAIX) expression by immunohistochemistry (IHC) i. Archival tumor tissue will be requested from patients who have undergone biopsy or tumor resection as part of routine clinical care prior to study participation to confirm diagnosis. Patients may undergo pre-treatment biopsy during the screening period if archival tissue is insufficient for baseline analysis.

• Tumor specimen may include nephrectomy or metastatic site specimen.

• At least one evaluable metastatic lesion as defined by RECIST 1.1 on zirconium-89 (89Zr)-girentuximab PET/CT

• At least one prior line of systemic therapy, including at least one prior treatment with anti PD-1 or PD-L1antibody

• Age ≥18 years

• KPS ≥ 70

• Adequate performance status and adequate organ function:

∙ ANC ≥ 1500 cells/μL

‣ WBC ≥ 2500/μL

‣ Platelet count ≥100,000/μL (without transfusion within 2 weeks prior to Cycle

∙ 1, Day 1; thrombopoietic agent use is allowed)

‣ Hemoglobin ≥9.0 g/dL (patients may be transfused or receive erythropoietic treatment to meet this criterion)

• AST, ALT, and alkaline phosphatase ≤ 2.5 x ULN, with the following exceptions:

∙ Patients with documented liver metastases: AST and/or ALT ≤ 5 x ULN

‣ Patients with documented liver or bone metastases: alkaline phosphatase ≤ 5 x ULN

• Serum bilirubin ≤ 2 x ULN

• a) Patients with known Gilbert disease who have serum bilirubin level ≤ 3 x ULN may be enrolled.

• INR and aPTT ≤ 1.5 x ULN

• a) This applies only to patients who are not receiving therapeutic anticoagulation; patients receiving therapeutic anticoagulation should be on a stable dose.

⁃ Creatinine clearance ≥ 40mL/min, as measured by the Cockcroft-Gault formula.

⁃ Women of childbearing potential and men are advised to practice double-barrier contraception until a minimum of 6 months after IV 89Zr-girentuximab or177Lu-girentuximab administration. Women of childbearing potential are advised to practice double-barrier contraception until a minimum of 5 months after nivolumab.

⁃ Signed consent form by the participant or a legally authorized representative (LAR).