The significance of circulating tumor cells in prostate cancer patients undergoing adjuvant or salvage radiation therapy

Background:following radical prostatectomy, success of adjuvant and salvage radiation therapy (rt) is dependent on the absence of micrometastatic disease. however, reliable prognostic/predictive factors for determining this are lacking. therefore, novel biomarkers are needed to assist with clinical decision-making in this setting. enumeration of circulating tumor cells (ctcs) using the regulatory-approved cellsearch system (css) is prognostic in metastatic prostate cancer. we hypothesize that ctcs may also be prognostic in the post-prostatectomy setting.methods:patient blood samples (n=55) were processed on the css to enumerate ctcs at 0, 6, 12 and 24 months after completion of rt. ctc values were correlated with predictive/prognostic factors and progression-free survival.results:ctc status (presence/absence) correlated significantly with positive margins (increased likelihood of ctcneg disease; p=0.032), and trended toward significance with the presence of seminal vesicle invasion (ctcpos; p=0.113) and extracapsular extension (ctcneg; p=0.116). although there was a trend toward a decreased time to biochemical failure (bcf) in baseline ctc-positive patients (n=9), this trend was not significant (hazard ratio (hr)=0.3505; p=0.166). however, ctc-positive status at any point (n=16) predicted for time to bcf (hr=0.2868; p=0.0437).conclusions:one caveat of this study is the small sample size utilized (n=55) and the low number of patients with ctc-positive disease (n=16). however, our results suggest that ctcs may be indicative of disseminated disease and assessment of ctcs during rt may be helpful in clinical decision-making to determine, which patients may benefit from rt versus those who may benefit more from systemic treatments.