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Cell-free DNA as a prognostic marker for response to taxan-based chemotherapy in patients with prostate cancer (CaP).

228 Background: PSA is of limited value for predicting response to chemotherapy in castration resistant CaP patients. Nevertheless there is no better biological marker to control therapy response. cfDNA showed significant results in prostae cancer diagnostics and predicting recurrence after radical prostatectomy. We analyzed for the first time the role of cfDNA in castration resistant CaP predicting response to chemotherapy.


METHODS
We analyzed cfDNA isolated from an EDTA blood sample from 58 patients taken before initiating a first or second-line taxan based chemotherapy. 54 (93,1%), 8 (13,8%) and 3 (5.1%) of the patients had bone, lymph node or parenchymatous metastases respectively. Patients were selected according to PSA response after at least 3 cycles of chemotherapy to 30% (A), 50% (B) and 80% (C) decrease under chemotherapy. The concentration of cfDNA at the beginning of the therapy was correlated to PSA resonse at the end of the treatment.


RESULTS
Mean PSA and cfDNA concentration at therapy initiation was 391 (0,1-2663)ng/ml and 32,5 (8,93-136,63)ng/ml. In group A there was a trend of higher cfDNA concentration in the patients not achieving a PSA decrease of at least 30% (24,6ng/ml versus 35.5ng/ml) not reaching statistical significance (p=0,078).


CONCLUSIONS
Patients with PSA decrease of less than 30% and PSA progression under chemotherapy have the poorest outcome. cfDNA is easy to investigate and is probably of importance to distinguish patients profiting from chemotherapy in a palliative setting. These data should be validated in a larger patient cohort.