Changing treatment landscape in the initial management of metastatic castrate-resistant prostate cancer (mCRPC): An Australian multi-centre retrospective study.

Background: The therapeutic armamentarium for mCRPC has rapidly expanded in recent yearswithmultiple novel agents gaining regulatory approval, supported by superior clinical outcome data and favourable toxicity profiles. The impact of these approvals on the local treatment landscape in Australia is unclear.Our objectivewas to characterize the change in prescribing habits in first-line mCRPC patients and other predictive factors that may have impacted these treatment decisions. Method(s): Retrospective data from patients diagnosed with mCRPC between 2013 and 2016 across four large Australian hospitals were collected. Baseline clinical factors and initial treatment decision at time of mCRPC development [watchful waiting (WW) vs immediate systemic therapy (IST)] were recorded. The WW cohort included intervention such as first-generation antiandrogens introduction and use of palliative radiotherapy. Categorical variables between cohorts were compared by chi-squared analysis (Fisher-exact test if expected frequency <5). Time-to-treatment post development of castrationresistance was compared for each year using the non-parametric Kruskal-Wallis test. Result(s):Our study identified 137 mCRPC patients, with clinicians opting for WW or IST in a 50:50 ratio. Median time-to-treatment in the WWand IST group was 9.7 and 1.0 month, respectively (P<0.001). IST patients were more likely to be symptomatic (P < 0.001), have shorter PSA doubling time (P = 0.003) and tended to being younger (analysis across four age levels; P=0.15). Therewas a significant transition away from WW to IST across the study period (P < 0.001), largely driven by the introduction of novel androgen receptor signalling inhibitors (ARSIs) in the first-line setting. Median time-to-treatment was statistically significantly different between years, H(3) = 20.127, P < 0.001. Conclusion(s): Clinicians are performing less WW at the development of mCRPC, instead favouring earlier introduction of systemic therapy. This