Abstract C9: Treatment response to abiraterone acetate (AA) in patients with castration-resistant prostate cancer (CRPC) based on circulating tumor cells (CTCs), prostate-specific antigen (PSA), and imaging
Authors: Bianchini Diletta , Reid Alison , Attard Gerhardt , De Bono Johann , Sandhu Shahneen , Mulick Amy Cassidy , Mukherji Deborah , Pezaro Carmel , Zivi Andrea , Omlin Aurelius , Sarvadikar Ajit , Thompson Emilda 
Published: May 2013

Background: AA, a potent oral irreversible inhibitor of CYP17A1, has been recently approved for patients with CRPC progressing after docetaxel. CTC count ≥ 5/7.5 ml correlates with worse survival in CRPC. In this analysis we evaluated PSA responses, radiological responses and CTC conversion rates in relation to patient outcome.

Methods: 141 patients (ECOG Performance Status 0-2; Median Age: 69.7; 85 post-docetaxel, 56 pre-docetaxel) treated with AA at the Royal Marsden NHS Foundation Trusts between December 2005 and March 2011 were included in this retrospective analyses. CTCs were enumerated using CellSearch at screening, baseline, at multiple time points during the study and at treatment discontinuation. PSA and imaging (Computer Tomography and Bone Scans) were obtained at the same time points as CTC collection. The Kaplan-Meier method was utilized for these analyses.

Results: Baseline CTCs of ≥ 5 cells/7.5 ml were detectable in 17/53 (32.1%) pre-docetaxel patients (3 inevaluable) and 58/77 (75.3%) post-docetaxel patients (8 inevaluable at baseline). CTC conversion (≥ 5 to &lt; 5 cells/7.5 ml) was observed in 10/17 (58.8%) pre-docetaxel patients and in 12/52 (23.1%) (6 inevaluable) post-docetaxel patients. PSA responses by PCWG II were observed in 16/22 (72.7%) of patients who attained a CTC conversion. PSA responses were seen in 8/47 (17.0%) patients in the absence of a corresponding CTC conversion. The median duration of radiological SD was 12.13 months (n=55) and 5.4 months (n=75) in patients with a baseline CTCs count of ≤ 5 cells/7.5mls and ≥ 5 cells/7.5 mls respectively. Overall, radiological stable disease was observed for a median of 6 months (95% CI: 4.2, 8.4; range 0.3, 35.6) beyond PSA progression in the 105 patients who experienced PSA progression. Radiological and clinical disease stability during treatment of ≥ 1 year, ≥ 2 years and ≥ 3 years was observed in 43/141 (30.5%), 21/141 (14.9%) and 12/141 (8.5%) respectively.

Conclusion: Radiological and clinical disease stabilization beyond PSA progression is seen in a significant proportion of patients treated with AA. CTCs conversion correlates with PSA response and radiological disease stability.

Citation Format: Diletta Bianchini, Alison Reid, Gerhardt Attard, Johann De Bono, Shahneen Sandhu, Amy Cassidy Mulick, Deborah Mukherji, Carmel Pezaro, Andrea Zivi, Aurelius Omlin, Ajit Sarvadikar, Emilda Thompson. Treatment response to abiraterone acetate (AA) in patients with castration-resistant prostate cancer (CRPC) based on circulating tumor cells (CTCs), prostate-specific antigen (PSA), and imaging [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr C9.