Can Contemporary Targeted Therapies Provide Clinically Meaningful Changes In Renal Cell Carcinoma Venous Tumor Thrombi?

390 Background: Renal cell carcinoma (RCC) tumor thrombus regression has been reported after treatment with contemporary targeted therapies. We sought to identify clinically meaningful changes in tumor thrombi in a series of patients treated with targeted therapies. Methods: A University of Texas M. D. Anderson institutional database was queried for patients treated with targeted therapy while the primary RCC remained in situ. The subset of patients with a vascular tumor thrombus was assessed for radiographic responses of tumor thrombi. Pathology was obtained from a percutaneous biopsy or the surgical specimen. The modified Clavien system was used to grade complications within 12 months of surgery. Clinically meaningful changes were defined as changes in the anatomic thrombus level or changes altering surgical approach. Results: A total of 178 patients were treated with targeted therapy with the primary tumor in situ. Venous tumor thrombus was present in 27% (n=48) and comprised our study cohort. The primary histology was clear cell in 75% of cases and 47/48 patients presented with metastatic disease. Prior to treatment, the tumor thrombus was within the renal vein (RV) in 60% (29/48-Level 0), the first 2 cm of the inferior vena cava in 10% (5/48-Level 1), > 2 cm above the RV in 21% (10/48-Level 2), at the level of the hepatics but below the diaphragm in 6% (3/48-Level 3), and above the diaphragm in 2% (1/48-Level 4). After a median duration of therapy of 2.75 months, clinically meaningful changes occurred in 25% of patients (12/48). Of these, progression occurred in 58% (7/12) while 42% (5/12) had regression of tumor thrombus. Fourteen patients (30%) received surgery after targeted therapy. Clavien categorized complications ≥ grade 3 occurred in 50% of surgical cases. No patient experienced a pulmonary embolism with treatment or during follow up. Conclusions: To our knowledge,this is the largest reported series of RCC patients with an in-situ venous tumor thrombus treated with targeted therapy. Although no patient experienced a pulmonary embolism, the use of targeted therapy with the primary goal of obtaining clinically meaningful reductions in tumor thrombi does not appear to be a promising therapeutic option. No significant financial relationships to disclose.