Pre-Therapy Visceral Metastases In Castrate Resistant Metastatic Prostate Cancer: Role In Tumor Progression.

e17586 Background: Visceral metastases in castrate resistant metastatic prostate cancer (mCRPC) are known to develop late in the course of disease and portend a poor prognosis. As patients with visceral metastases still derive a clinical benefit to treatment, understanding patterns of progressive disease (PD) may help differentiate important disease phenotypes in mCRPC. The aim of our study was to evaluate the differences in anatomic sites of PD in patients with pretreatment visceral or bone metastases on time to progression (TTP). Methods: A retrospective review of anonymized patients enrolled in phase 2 and 3 clinical trials was performed. Patients were excluded if lacked Tc bone scan or CT chest, abdomen and pelvis (CT CAP) at baseline. Bone disease was defined by automated bone scan lesion area (BSLA) criteria. All CT CAPs per clinical trial protocol were assessed by RECIST 1.1. Soft tissue PD was noted as target, non-target lesion growth and/or presence of new lesions by anatomic site. Bone PD was defined by > 20% increase in BSLA score. Results: Of the 169 subjects that met our selection criterion, visceral disease was present at baseline in 90 patients (53%). Baseline BSLA score was 90474 mm² in visceral and 80348 mm² in non-visceral patients (p = 0.395). Disease progression occurred in 93 patients (55%). With baseline visceral disease, PD was a result of BSLA in 26 (51%) and visceral disease only in 11 (22%) of patient. Lacking visceral disease at baseline resulted in PD by BSLA in 26 (62%) and visceral disease only in 3 (7%) of patients. There was no significant difference in PFS for baseline visceral/non-visceral involvement; median PFS = 4.5 months in visceral; median PFS = 4.34 months in non-visceral (HR = 1.28; p = 0.244). Conclusions: Patients with visceral disease may still derive a similar clinical benefit from treatment to those without. While the presence of baseline visceral disease was associated with higher rates of PD by visceral involvement, PD by bone disease remained the most common cause of PD regardless of presence of baseline visceral metastases.