MP73-04: External validation of a risk score predicting failure after salvage focal therapy for localized radiorecurrent prostate cancer: an analysis from the FOcal RECurrent Assessment and Salvage Treatment (FORECAST) trial
Introduction: Patient selection for salvage focal therapy might be improved with risk prediction tools. For men with localized radiorecurrent prostate cancer, we used the FORECAST study to externally validate our previously published risk score for predicting failure post-salvage focal therapy (doi: 10.1016/j.urolonc.2017.08.022). Methods: Men were included from the prospective, multicentre FORECAST trial (NCT01883128) with =T3bN0M0 radiorecurrence who had undergone salvage focal high-intensity focused ultrasound (HIFU) or cryotherapy (2014-2018). Recurrence was diagnosed by transperineal template mapping and MRI-targeted biopsies. Staging comprised bone scan and choline PET/CT. The outcome was a composite failure, defined as biochemical failure, localized/distant disease on re-imaging, positive re-biopsy, commencement of systemic hormones or chemotherapy, or cancer-related death. Variables from the original multivariable Cox model were Gleason score, disease-free survival interval, T-stage, prostate volume, and PSA. Model performance at 2 years post-treatment was assessed via discrimination (C-index), calibration plot, and decision curve analysis. Results: 71 men were included (HIFU n=51; cryotherapy n=20). 37 experienced failure (biochemical failure n=20; recurrent disease on imaging n=13; positive biopsy n=2; starting systemic hormones/chemotherapy n=2). Median time-to-failure was 0.93 years (IQR 0.65-1.04). C-index was 0.64 (95%CI 0.53-0.73). The calibration plot demonstrated some overestimation of failure-free survival at lower predictions, and underestimation at higher predictions (Fig.1). Compared to a ‘treat all’ approach, the model had improved net benefit at risk thresholds =0.43, equating to net benefit for a clinician who would treat at most 3.3 men for 1 of them to be failure-free at 2 years. Conclusions: In this external validation, this risk score performed modestly in predicting failure post-salvage focal therapy. This score could be used to identify high-risk patients who may benefit from treatment escalation or multimodal treatment. SOURCE OF Funding: Funded by the Pelican Cancer Foundation, the US National Institutes of Health, and the UK Medical Research Council.
