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.
Evaluation of cell free circulating DNA in plasma by digital PCR for early diagnosis in Peruvian breast cancer patients
