Determining viability of circulating tumor cells (CTCs) as a predictive biomarker for response in patients (pts) with metastatic castrate resistant prostate cancer (mCRPC) treated with Radium 223 (Ra).

Abstract

e16051 Background: Ra improves survival in bone symptomatic mCRPC pts. Response assessment to Ra is difficult because of low PSA responses and pts are monitored through alkaline phosphatase (ALP) and clinically. CTCs count is a well-known predictive and prognostic biomarker in mCRPC. The aim of the study was to assess CTCs as a predictive biomarker for response to Ra therapy. Methods: Blood samples were collected from 46 pts with mCRPC treated with Ra at 8 hospitals in Spain between February and October 2014. Samples were obtained at baseline, at cycle 3 and at progression and were centrally analyzed using the CellSearch System. Statistic analysis was done with SAS v9.3 program. CTCs outcome at cycle 3 was defined as: response: decrease > 50% in relation to baseline or ≤ 5 CTCs; progression: increase > 50% or > 5 CTCs; and stabilization: absence of either response or progression. Results: We collected samples at baseline, cycle 3 and progression from 42, 32 and 18 pts respectively (see table). Pts charact...