A Phase 2 Study Of Cabozantinib In Metastatic Castrate Resistant Prostate Cancer (Mcrpc) With Visceral Metastases (Vm) With Very Small Nuclear Circulating Tumor Cell (Vsnctc) Association Studies.

208 Background: Cabozantinib is a multi-targeted tyrosine kinase inhibitor (TKI) that has recognized clinical activity in mCRPC. While phase 3 studies did not show a significant improvement in overall survival (OS), patients with VM had improved OS compared to those with only osseous metastases in subgroup analysis. Our group has also identified a subgroup of CTCs strongly associated with the presence of VM (Chen, Cancer 2015). We hypothesized that cabozantinib would yield clinical benefit and changes in vsnCTC counts would reflect disease behavior. Methods: This study was designed as an open label study of cabozantinib 60 mg daily, for mCRPC patients with visceral disease. The primary endpoint is clinical benefit rate (radiographic stable disease + partial response (PR) by RECIST 1.1) at 12 weeks (CBR12). Serum PSA concentrations were not used as a primary endpoint. CTCs were enumerated by NanoVelcro CTC Assay and characterized using published methods. Results: Thirteen patients have completed at least 8...