Project Summary While there are many treatment options for patients with metastatic RCC, it is still a deadly disease with considerable mortality. RCC can be much more effectively treated if it is detected early when it is amenable to surgery. To date there is no biomarker for RCC. Additionally, A specific and sensitive circulating biomarker could not only help detect this cancer earlier but could also aid in the diagnosis and monitoring of disease. This proposal seeks to test the utility of circulating kidney injury molecule-1/ T cell immunoglobulin mucin domain-1 (KIM-1/ TIM-1) as a blood test that can be used to follow patients with small renal masses and with the goal of safely avoiding or delaying surgery. We will also measure KIM1 in patients with resected RCC with the goal of identifying a high-risk patient population most likely to benefit from adjuvant therapy after nephrectomy for localized disease. This proposal will also test KIM-1 as a blood test that can help follow response to therapy for metastatic disease. To prepare for submission our team has spent considerable time and effort in identifying readily available patient samples to answer our questions. In this proposal we are poised and have samples available to address all of these questions. We hope that in the future, prospective trials will test KIM-1 in these settings but at this time, rigorous testing in these retrospective cohorts will provide the groundwork for these future studies.