PURPOSE: Chemotherapy is an integral part of the treatment of castration 
resistant prostate cancer. With the introduction of new drugs the need to 
identify nonresponders is increasing. To our knowledge there are no prognostic 
parameters to date for use upon the initiation of any treatment.
MATERIALS AND METHODS: cfDNA was isolated from a serum specimen before 
chemotherapy. Its value was correlated to recurrence-free and overall survival 
using Kaplan-Meier curves. Univariate and multivariate Cox regression analysis 
was performed to identify independent predictors.
RESULTS: Of 59 men 48 (81.4%) had a measurable prostate specific antigen 
decrease from baseline. Median followup was 15.0 months (range 2.4 to 58.4). The 
median cfDNA concentration in all men in this study was 27.71 ng/ml (mean 
32.64). A threshold of 55.03 ng/ml was significantly associated with a poor 
prostate specific antigen response of less than 30% (p = 0.005). On univariate 
and multivariate analysis circulating cfDNA was an independent predictor of 
overall survival (HR 0.36, 95% CI 0.13-0.97, p = 0.044 and HR 0.34, 95% CI 
0.12-0.91, p = 0.032, respectively). Limitations of the study are its 
retrospective character, and first and second line therapies.
CONCLUSIONS: Our trial shows that the cfDNA concentration before therapy may be 
a useful predictive and prognostic biomarker for prostate specific antigen 
response and survival.