Purpose: To investigate the relationships between circulating tumor cells (CTCs), free circulating DNA
(fcDNA) and biochemical response in prostate cancer patients treated primarily versus salvage radiotherapy
(RT).
Methods and Materials: Blood was collected prospectively from patients, enrolled in two institutional
Phase II trials for primary and salvage RT. Three blood samples were collected at: (i) prior to treatment [RT
or androgen deprivation therapy (ADT)], (ii) last week of RT, and (iii) three months post-RT. CTCs were
quantified in 31 samples from 12 primary patients and 30 samples from 12 salvage patients; fcDNA were
analyzed in 11 primary (28 samples) and 5 (9 samples) salvage patients. CTCs were visualized by
immunofluorescence after microfilter capture and fcDNA was quantified using real-time Polymerase chain
reaction (PCR). CTCs and fcDNA were correlated with early biochemical response by subdividing patients
into early favorable and unfavorable response at 3 months after RT.
Results: For those treated primarily, there was a direct correlation with CTC counts and prostate specific
antigen (PSA) pre-RT that changed to a reciprocal relationship 3 months post-RT. CTCs increased
significantly (p=0.03) at 3 months after primary RT in the biochemical favorable patients, while no
significant association was observed for fcDNA. Correspondingly, post-RT fcDNA levels were inversely
related to CTC counts. In salvage patients, the number of CTCs was related to pre-RT PSA, but it was not
correlated to RT response. In post-RT series, a significant direct correlation was observed between CTCs
and PSA.
Conclusion: Our preliminary studies suggest that RT affects CTC counts, which are thus associated with
prostate cancer biochemical response. A larger cohort with longer follow-up will be needed to establish the
association with more recognized treatment endpoints.
The Role of Cell-Free Circulating DNA in the Diagnosis and Prognosis of Breast Cancer
