The goal of this clinical trial is to better tell apart whether kidney tumors are benign (not cancer) or malignant (cancer) based on a biopsy or imaging tests and ask patients how they feel about decisions they make about treatment of their kidney tumor.

The main objectives are:

To estimate and compare the diagnostic accuracy of renal mass biopsy alone, PEER (with renal mass biopsy), and 99mTc-sestamibi SPECT/CT (with renal mass biopsy for hot tumors) to differentiate malignant and benign renal tumors.

To estimate and compare the diagnostic accuracy of renal mass biopsy, PEER (with renal mass biopsy), and 99mTc-sestamibi SPECT/CT (with renal mass biopsy for hot tumors) to differentiate oncocytoma from chromophobe RCC.

Participants will be asked to complete survey questions related to their health and kidney tumor at the start and end of the study. These can be done on paper, electronically, or by telephone.

The investigators are asking the participant to take part in this research study because they were diagnosed with a kidney tumor. Kidney tumors can be benign (not cancer) or malignant (cancer) and the investigators hope to figure out how to better tell them apart before surgery or other treatment.

The investigators hope to better tell apart whether kidney tumors are benign (not cancer) or malignant (cancer) based on a biopsy or imaging tests and ask patients how they feel about decisions they make about treatment of their kidney tumor.

Biopsy is a standard test to determine if a tumor is cancerous before making a treatment decision.

The imaging test (99mTc-sestamibi SPECT/CT) the investigators are studying has been studied before and found to help identify benign kidney tumors. It is not approved by the Food and Drug Administration (FDA) for imaging kidney tumors. It is FDA approved for use in imaging the heart and breasts. It has been studied for use in parathyroid gland imaging.

The participant will be asked to complete survey questions related to their health and kidney tumor at the start and end of the study. The participant will receive a 99mTc-sestamibi SPECT/CT scan (if they have not had one already) for research purposes. The participant will receive a biopsy of the kidney tumor (if they have not had one already) as part of their routine clinical care. The participant will then receive treatment of the kidney tumor as determined by consultation with their doctor.

Inclusion Criteria:

• Participants diagnosed with a clinically localized (cT1) renal tumor ≤7cm in size with a solid component suspicious for malignancy based on cross-sectional imaging
• Pre-existing CT images of the mass with and without contrast or planned CT to ensure both with and without contrast images of the mass have been obtained within a 365-day window
• Participants must be greater than or equal to 18 years of age
• Eligible or planned to undergo partial or radical nephrectomy as determined by primary urologist
• Eligible or planned to receive renal mass biopsy as determined by primary urologist
• Estimated glomerular filtration rate of ≥30 ml/min/1.73 m2 as calculated by the CKD-EPI (Chronic Kidney Disease-Epidemiology Collaboration) Equation

Exclusion Criteria:

• Participants must not be pregnant (as determined by local policy by radiology / imaging center)
• Participants must not have evidence of clinical nodal or distant metastasis.
• Participants must not have had a history of other malignancy with concern for renal metastasis.
• Participants must not have any known allergy to technetium or sestamibi.

Participants will be 18 years of age and older, male or female and diagnosed with a kidney tumor. Kidney tumors can be benign (not cancer) or malignant (cancer).