2527 - Circulating Tumor Cells (CTC) count and Prostate-Specific Antigen (PSA) response measures in metastatic Castration-Resistant Prostate Cancer (mCRPC) patients (pts) treated with Docetaxel (Doc)

Background

Clinically meaningful measures of response are needed in mCRPC. Post-treatment CTC decline have shown to be superior to PSA response in determining outcome in pts treated with AR signalling inhibitors. We compared the performance of CTC and PSA measures of response in mCRPC Doc-treated pts.

Methods

Baseline and post-treatment (6 to 9 weeks) CTC of mCRPC pts treated with Doc at first or second-line in a prospective study were determined with CellSearch^TM platform. CTC response was defined: 30% decline from baseline (CTC30%), conversion (≥5 to < 5; CTCConv) or decline to 0 CTC in pts with >0 baseline CTC (CTC0). PSA response was determined at 12w as 30% (PSA30) or 50% decline (PSA50) from baseline. Cox-regression model were used to evaluate the association of baseline CTC (BLCTC), CTC response and PSA response measures with overall survival (OS), progression-free survival (PFS) or time to PSA progression (TTPP). C-index were used to evaluate the performance of each of the Cox regression model.

Results

80 pts had evaluable BLCTC, 52 had evaluable post-treatment CTC count. Of 80 eligible pts, 53 (66.3%) received Doc at first-line. Median OS was 19 m (95%CI:16.4-21.8); median BLCTC was 7. BLCTC were associated with bone mts, higher PSA, ALP and LDH, and lower albumin levels. BLCTC was associated with OS (HR: 3.5; p < 0.001), PFS (HR: 1.98; p = 0.001) and TTPP (HR: 1.8; p = 0.001). CTC (CTC30%, CTCConv, CTC0) but not PSA (PSA30, PSA50) response measures were significantly associated with OS. C-index values were higher for CTC resp endpoints (Table). 24 pts had discordant PSA30 and CTC30% response; longer OS (18.4 vs 8.4m; p = 0.188) was observed in pts with CTC30% resp, without PSA30 resp.Table:

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Conclusions

Baseline CTC were associated with OS, PFS and TTPP. CTC response measures were significantly associated with outcome, and showed a greater performance than PSA response measures in mCRPC Doc-treated pts.

Editorial acknowledgement

Legal entity responsible for the study

Spanish National Cancer Research Center (CNIO) and The Institute of Cancer Research (ICR).

Funding

Has not received any funding.

Disclosure

R. Lozano Mejorada: Honoraria (self): Roche, Janssen-Cilag, Bayer; Research grant / Funding (institution): Bayer, Janssen-Cilag; Travel / Accommodation / Expenses: Roche, Janssen-Cilag, Astellas Pharma. D. Lorente: Honoraria (self): Janssen-Cilag, Bayer, Astellas Pharma, Sanofi; Advisory / Consultancy: Janssen-Cilag, Bayer, Sanofi; Travel / Accommodation / Expenses: Sanofi, Astellas, Janssen-Cilag, Celgene. E. Castro: Honoraria (self): Astellas Pharma, Janssen-Cilag, AstraZeneca, Bayer, Pfizer; Advisory / Consultancy: Bayer, Janssen-Cilag, AstraZeneca, Clovis Oncology; Research grant / Funding (institution): Janssen-Cilag, AstraZeneca, Bayer; Travel / Accommodation / Expenses: Bayer, Janssen-Cilag, Roche, Astellas Pharma. N. Romero Laorden: Honoraria (self): MSD, Sanofi-Aventis, Astellas, Janssen-Cilag; Travel / Accommodation / Expenses: Bayer, Janssen-Cilag, Roche, PharmaMar; Research grant / Funding (institution): Bayer, Astellas, Janssen-Cilag, Sanofi-Aventis. E. Almagro Casado: Honoraria (self): MSD; Travel / Accommodation / Expenses: BMS. M. Saez: Honoraria (self): Bristol-Myers Squibb, Pfizer, Novartis, Bayer, Janssen-Cilag, Sanofi-Aventis, Astellas Pharma, Ipsen, EUSA Pharma; Advisory / Consultancy: Bristol-Myers Squibb, Pfizer, Novartis, Bayer, Janssen-Cilag, Sanofi-Aventis, Astellas Pharma, Ipsen, EUSA Pharma; Travel / Accommodation / Expenses: Bristol-Myers Squibb, Pfizer, Novartis, Bayer, Janssen-Cilag, Sanofi-Aventis, Astellas Pharma, Ipsen, EUSA Pharma. D. Olmos Hidalgo: Honoraria (self): Janssen-Cilag, Bayer, Sanofi; Advisory / Consultancy: Bayer, Janssen-Cilag, AstraZeneca, Clovis Oncology; Research grant / Funding (institution): Bayer, Janssen-Cilag, AstraZeneca, Roche/Genentech, Medications/Pfizer, Astellas, Tokai, MSD, GSK; Travel / Accommodation / Expenses: Bayer, Janssen-Cilag, Ipsen. All other authors have declared no conflicts of interest.