Genomic And Imaging Biomarkers Associated With Cabozantinib Therapy In Metastatic Castrate Resistant Prostate Cancer (Mcrpc).

212 Background: Cabozantinib (C) is a c-met and vascular endothelial growth factor receptor inhibitor that demonstrated remarkable responses on bone scan, but failed to demonstrate overall survival benefit. We studied the dynamics of biomarker changes with imaging and biopsies pre- and post-therapy with C to explore predictors of efficacy. Methods: Eligibility included mCRPC patients (pts) with normal organ function and performance status 0-2. C 60 mg orally was administered daily. Pretherapy and 2 weeks post, 99mTc-labeled bone scans (BS), positron emission tomography with 18F-sodium fluoride (NaF-PET) and 18F-(1-(2′-deoxy-2′-fluoro-β-D-arabinofuranosyl) thymine (FMAU-PET) scans were conducted. The maximum tumor standardized uptake values (SUVmax) were measured for the 5 most active lesions in at least 3 skeletal areas with each tracer. Tumor biopsies were conducted, and bone markers were measured. Results: 20 evaluable pts, 5 African American and 15 Caucasian were enrolled. Median age was 69 years, 11 h...