Modulation of the Bone Immune Microenvironment Following Cabozantinib Treatment of Bone Metastatic Clear Cell Renal Cell Carcinoma: Proof of Concept Study

The goal of our study is to explore how treatments affect the bone immune microenvironment and determine the best treatment options for patients with metastatic kidney cancer to the bone. This could prevent skeletal complications and improve patient outcomes.

Primary Objectives: 1. To assess safety of obtaining biopsy within close time frame of cabozantinib treatment. 2. To evaluate the success rate of obtaining serial biopsies of bone metastases. Success is defined as viable single cell sequencing of bone biopsy samples at baseline and after 8 weeks of treatment. 3. To quantify the fold change in M1:M2 macrophage population in serial biopsies from renal cell carcinoma bone metastases. Secondary Objectives: 1. To compare the M1:M2 macrophage population at baseline and on therapy in paired bone versus non-bone metastatic sites. 2. To compare CD8+, Granzyme+ cells on multiplex immunofluorescence at baseline and on therapy in paired bone versus non-bone metastatic sites. 3. To describe serum marker changes over time while on therapy for bone metastasis including bone alkaline phosphatase, osteopontin, procollagen type I amino-terminal propeptide (PINP), and beta-isomer of carboxy-terminal telopeptide of type I collagen (â-CTX) and association with response and progression. 4. To describe overall response rate (proportion of participants who achieve a best response of complete response or partial response using RECIST 1.1 criteria), time until progression (time from initiation of systemic treatment to the date of documented disease progression), and progression-free survival (time between the first date of systemic treatment to first date of documented progression or death due to any cause). 5. To describe incidence of skeletal related events defined as a composite of pathologic fracture, spinal cord compression, radiation or surgery to bone, and hypercalcemia of malignancy. 2.3 Exploratory Objective: 1\. OPTIONAL: To describe findings in Extreme CT scan at baseline and/or at 6 months and association with skeletal related events.