193 Background: Outcomes of patients (pts) undergoing CHT for mHSPC are heterogeneous, with some rapidly developing castration-resistance (CRPC). While AVPC ("anaplastic") features are described in CRPC, less is known in the mHSPC setting. In this multi-institutional cohort, we explored pre-treatment factors associated with poor outcome. Methods: De-novo mHSPC pts treated with CHT from June 2014 to July 2017 at The Ottawa Hospital Cancer Centre (TOHCC) and London Regional Cancer Centre (LRCC) were retrospectively identified. AVPC features (defined below) were collected and cumulatively scored (0, 1, or 2+), along with baseline, treatment and outcome data. Statistical comparisons utilized Cox regression analysis and Kaplan-Meier method for association with CRPC and survival. Results: 92 pts (58 TOHCC, 34 LRCC) met inclusion for study; 83 (90%) had "high-volume" disease (≥4 bone lesions; or ≥1 visceral metastasis), 69/73 (95%) prostate biopsies scored Gleason 8-10, and 55 (60%) had AVPC features: >5 cm nodal/pelvic mass (28), visceral metastases (21), lytic bone metastases (16), elevated LDH (12), low PSA (4), or neuroendocrine differentiation (2). Pre-docetaxel PSA fall of