The use of the PSA as a prostate cancer screening tool has been a controversial issue for many years. Within the last year the issue has again come to the forefront of the public awareness, especially because of the recent move of the U.S Preventative Task Force to discourage using the PSA as a screening tool . One of the ways that has been used to approach this question is to develop a better bio-marker to serve both as a screening tool and as a predictor of the responsiveness to treatment. If such a marker could be identified, we could make better decisions about who should be treated and for how long a specific treatment should be continued. This better biomarker could reduce the suffering brought about by unnecessary treatment as well as save many dollars.
Recently, circulating tumor cells (CTC’s) have been evaluated to serve as this possible marker. Studies have shown that in early stages of cancer it can begin the process of shedding cancer cells into the circulatory system. (Okegawa T, Nutahara K, etal; Prognostic Significance of Circulating Tumor Cellsin Patients with Hormonal Refractory Cancer, J Urol, March 2009. 181:1091-1097). These CTC’s can provide a handle into the intrinsic property of the tumors offering valuable information that can inform patient management (Danila, D, Heller G, etal, Circulating Tumor Cell Number in Progression, castrate-Resistant Prostate Cancer, Clinical Cancer Res, December 2007; 13(23) 7053-7).
Little known and never discussed is the decision of the FDA in 2008 to approve the CellSearch (Verdix, NH) System to count these circulating tumor cells to predict survival and monitor treatment in men with advanced prostate cancer. The Bono, etal trial (de Bono, Schere H, etal. Circulating Tumor Cells Predict Survival Benefit from Treatment in Metastatic Castrate Resistant Prostate Cancer. Clin Cancer Res 2008;(19) 6302-6309) that actually led to the CellSearch FDA approval showed that CTC numbers is a very strong predictor of survival for men who are castrate resistant. Additional research showed that when compared to PSA scores, CTC scores were clearly a more robust system to measure progression than was the PSA ( Scher, H, Jia X, etal. Circulating Tumor Cellsas as Prognostic markers in Progressive, Castrate resistant Prostate Cancer; a reanalysis of IMMC338 trial data, The Lancet Oncology, March 2009; 10(3) 233-239).
At the last ASCO Conference (June 2011) the final analysis of the Abiraterone/prednisone (Zytiga) trial concluded that both baseline and the intermediate data that CTC levels after initiating therapy were key predictors of overall survival.
So why are our oncologists continued to be married to the PSA test?
Joel T. Nowak, M.A., M.S.W.