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Prostate-specific Antigen Decline After 4 Weeks of Treatment with Abiraterone Acetate and Overall Survival in Patients with Metastatic Castration-resistant Prostate Cancer
The availability of multiple new treatments for metastatic castration-resistant prostate cancer (mCRPC) mandates earlier treatment switches in the absence of a response. A decline in prostate-specific antigen (PSA) is widely used to monitor treatment response, but is not validated as an intermediate endpoint for overall survival (OS).
To evaluate the association between early PSA decline and OS following abiraterone acetate (AA) treatment.
Design, setting, and participants
We identified mCRPC patients treated with AA before or after docetaxel at the Royal Marsden NHS Foundation Trust between 2006 and 2014. Early PSA decline was defined as a 30% decrease in PSA at 4 wk relative to baseline, and early PSA rise as a 25% increase.
Outcome measurements and statistical analysis
Association with OS was analyzed using multivariate Cox regression and log-rank analyses. Spearman's rho correlation coefficient (r) was calculated to evaluate the association between PSA changes at 4 wk and 12 wk.
Results and limitations
There were 274 patients eligible for this analysis. A 30% PSA decline at 4 wk was associated with longer OS (25.8 vs 15.1 mo; hazard ratio [HR] 0.47, p < 0.001), and a 25% PSA rise at 4 wk with shorter OS (15.1 vs 23.8 mo; HR 1.7, p = 0.001) in both univariate and multivariable models. The percentage PSA decline at 4 wk was significantly correlated with the percentage PSA change at 12 wk (r = 0.82; p < 0.001). Patients achieving a 30% PSA decline at 4 wk were 11.7 times more likely to achieve a 50% PSA decrease at 12 wk (sensitivity 90.9%, specificity 79.4%). Limitations include the retrospective design of this analysis.
Patients not achieving 30% PSA decline after 4 wk of AA have a lower likelihood of achieving PSA response at 12 wk and significantly inferior OS. Prospective multicentre validation studies are needed to confirm these findings.
Prostate-specific antigen (PSA) is commonly used to evaluate response to treatment in metastatic castration-resistant prostate cancer. Expert recommendations discourage reliance on PSA changes earlier than 12 wk after treatment initiation. Our data suggest that early PSA changes are associated with survival in patients receiving abiraterone acetate.
Keywords: Abiraterone acetate, Metastatic castration-resistant prostate cancer, Prostate-specific antigen.
The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton, UK
⁎ Corresponding author. The Institute of Cancer Research, The Royal Marsden NHS Foundation Trust, Downs Road, Sutton, Surrey SM2 5PT, UK. Tel. +44 208 7224028; Fax: +44 208 6427979.
© 2016 European Association of Urology, Published by Elsevier B.V.