REDECT 2: REnal Masses: Pivotal Trial to DEteCT Clear Cell Renal Cell Carcinoma With PET/CT

Inclusion Criteria: 1. ≥18 years of age. 2. Presence of indeterminate cT1 renal mass by screening CT with and without contrast or MRI with and without contrast (MRI only if CT is contra-indicated). 3. Negative serum pregnancy test; to be performed on female patients of childbearing potential within 24 hours prior to receiving investigational product. 4. Recovered from toxicity of any prior therapy to grade 1 or better. 5. Able to take oral medication (KI). 6. Written informed consent available. Exclusion Criteria: 1. Renal mass known to be a metastasis of another primary tumor. 2. Known histology of renal mass (e.g. by biopsy). 3. Active non-renal malignancy requiring therapy during the time frame of individual patient study participation. 4. Chemotherapy, radiotherapy, or immunotherapy within 4 weeks prior to Iodine (124I) Girentuximab infusion on Day 0 or continuing adverse effects (\>grade 1) from such therapy. 5. Exposure to murine proteins or chimeric antibodies within the last 5 years. 6. Intercurrent medical condition that may limit patient's study participation or compliance. 7. History of autoimmune hepatitis. 8. Mental impairment that may compromise the ability to give informed consent and comply with the requirements of the study. 9. Participation in any other clinical trial involving another investigational product within 4 weeks prior to enrollment. 10. Women who are pregnant or breastfeeding. 11. Contraindication to KI intake (see package insert/Appendix VI). 12. Hyperthyroidism, or Grave's Disease. 13. Contraindication for PET/CT.