LAUSR

270 Background: While D has been shown to prolong survival and improve quality of life in men with mCSPC in clinical trial settings, less is known about its effectiveness in the RW setting. Furthermore, it is uncertain whether the timing of D affects toxicity and outcome. We aimed to identify effectiveness and toxicity outcomes as well as patient (pt) characteristics and prescribing patterns at our institution. Methods: In this retrospective chart analysis, we identified 70 pts with mCSPC who were treated with D between June 2014 and September 2018 at an academic cancer centre in Toronto. The main outcomes studied included time to castrate resistance (TCR), change in PSA, number of cycles completed, and rates of febrile neutropenia (FN). We also analyzed pt subgroups including pts starting D <50 days after the start of androgen deprivation therapy (ADT) versus those starting >50 days after ADT initiation. Results: The median age of our pts was 69 (IQR: 64-74). The median follow-up time was 598 days. 79% of pts had high volume disease per CHAARTED criteria, 73% had de novo metastatic disease and 85% had bone-only disease. The median TCR from the start of ADT was 12.3 months. The median change in PSA from pre-ADT to post-D nadir was 99%. The mean D dose intensity was 86% of the ideal dose and 91% of pts completed all 6 cycles of D. 11% of pts were diagnosed with FN during treatment. 6% of pts required treatment delays and 19% required toxicity-related dose reductions. Subgroup analysis showed that patients (n=41) who received D >50 days from the start of ADT did not have significant differences in TCR, rates of FN, need for a decrease in dose intensity or treatment delays compared to those starting <50 days after ADT (n=29). Conclusions: D can be delivered safely in RW pts, with low rates of FN, however, there is evidence of an efficacy-effectiveness gap with a shorter TCR compared to that observed in CTs. The timing of D (<50 days vs. >50 days) does not appear to have an impact on outcome or toxicity.