Association of plasma tumor DNA (ptDNA) with increased risk of venous thromboembolism (VTE) in metastatic castration resistant prostate cancer patients (mCRPC)

5048 Background: Cancer is a risk factor for VTE. In mCRPC, ptDNA is an independent predictor of outcome ( Romanel, Sci Transl Med 2015; Conteduca, Br J Cancer 2020). We firstly aimed to investigate the association between ptDNA and VTE in mCRPC men treated with androgen receptor signaling inhibitors (ARSI) Methods: This prospective biomarker study included mCRPC patients treated with abiraterone and enzalutamide from April 2013 to December 2018. We excluded patients with a previous VTE history and/or ongoing anticoagulation. Targeted next-generation sequencing was performed to determine ptDNA fraction from pre-treatment plasma samples. Assessment of VTE risk based on survival analysis was performed using cumulative incidence function and estimating sub-distributional hazard ratio (SHR) Results: Median age of 180 enrolled patients was 74 years (range 42-90). Of these, 60 (33.3%) were chemotherapy-naive. At a median follow-up of 58 months (range 0.5-111.0), 21 patients experienced VTE (venous thrombosis and/or pulmonary embolism) with a cumulative incidence of VTE at 12 months of 17.1% (95% CI 10.3-23.9). Before starting ARSI, ptDNA fraction above median value of 0.175, presence of visceral metastasis (mets), prior chemotherapy and serum lactate dehydrogenase (LDH) were significantly associated with higher incidence of VTE compared with patients with no thrombosis (12-month estimate, 18.6 vs 3.5%, P=0.0003; 44.4 vs 14.8%, P=0.015; 24.7 vs 4.5%, P=0.006; and 30.0 vs 13.5%, P=0.050, respectively). In the multivariate analysis (Table) including baseline ptDNA level, visceral, liver and lung mets, number of lesions, LDH, high ptDNA fraction was the only independent factor associated with the risk of thrombosis (HR 5.78, 95% confidence interval [CI] 1.63-20.44, P=0.006). All these patients received anticoagulant therapy for VTE. No ARSI discontinuation and VTE-related death were reported, and no significant difference in progression-free/overall survival was observed in mCRPC patients with and without VTE. Conclusions: These results suggest that baseline ptDNA fraction in mCRPC patients treated with ARSI is associated with increased risk of VTE. These patients may be followed up more closely for the risk of VTE and the need for a primary thromboprophylaxis should be taken into account in mCRPC with elevated ptDNA concentration. Validation of these findings in larger multicenter trials is warranted.[Table: see text]