Multi-center study evaluating circulating tumor cells (CTCs) as a surrogate for survival in men treated for castration refractory prostate cancer (CRPC)

Abstract

5016 Background: Monitoring CTCs in patients undergoing therapy for metastatic breast cancer is an effective means to predict outcome and monitor treatment. The primary endpoint of this prospective multi-center study was to demonstrate a significant relation between the presence of CTCs and survival in men treated for CRPC. Methods: 276 patients with diagnosed CRPC, PSA progression, and an ECOG score of 0–2 about to begin initial or salvage chemo and/or combination therapy were enrolled. CTCs were enumerated with the CellSearch System in blood drawn pre-treatment and monthly thereafter for up to 18 months. Patient data were collected and maintained by an independent CRO. Median overall survival (OS) was determined for patients with =5 CTC /7.5mL at baseline and specified intervals. Results: Of 240 evaluable patients, 142 (59%) are alive - mean follow-up 11.4 ± 4.4 months. Median OS (in months) and significance between the two groups (logrank p-value) at different time points after the initiation of therapy are indicated in the table . Median OS for 40 (19%) patients with a reduction of CTCs below 5 CTCs 2–5 weeks after initiation of therapy was significantly longer as compared to those 78 (38%) patients that remained above 5 CTCs (>20 vs. 9.3mth, p=0.0000) and was not significantly different from the 83 (40%) patients with 20 vs. >20mth, p=0.2725). In multivariate analyses, which included stage at diagnosis, age, ECOG, Gleason score, LDH, Alkaline Phosphotase, and PSA, CTCs remained the most significant independent predictor of outcome. Conclusions: CTC levels in CRPC patients are a strong predictor of OS. The persistence of CTCs after initiation of therapy suggests that the patients are deriving less than optimal benefit from their current therapy. CTC levels may be a valid surrogate end-point in monitoring response to chemotherapy. [Table: see text] No significant financial relationships to disclose.