Preliminary results of a telomerase-based circulating tumor cell assay in prostate cancer patients undergoing definitive radiotherapy.

Abstract

139 Background: Circulating tumor cell (CTC) analysis provides a minimally invasive tool to serially assess a primary tumor and its response to treatment, which may assist management. We conducted a pilot study among patients with localized prostate cancer to examine the potential effectiveness of a novel telomerase-based CTC assay for tracking the response to definitive radiotherapy (RT). Methods: The assay relies on processing and exposure of peripheral blood samples to an adenoviral vector, utilizing the human telomerase promoter to drive the expression of a fluorescent reporter. Such a system results in high specificity and sensitivity for prostate cancer cell detection since telomerase is elevated in almost all malignancies, but not in normal cells. Peripheral blood samples from patients with localized prostate cancer were obtained up to one month prior to initiating RT (pre-RT), one-half to two-thirds through completion of the RT course (mid-RT), and after completion of RT (post-RT, 3 to 6 months following completion of treatment). Fifty seven subjects were enrolled on this study, with a mean age of 67 (SD 6.7 years). Fifteen had low-risk, 25 had intermediate risk, and 17 had high risk disease at the time of diagnosis. Twenty subjects received androgen suppression. Results: We successfully detected CTCs in the majority of patients undergoing definitive radiotherapy for localized prostate cancer of varying Gleason scores (GS), risk status, and disease stages. The mean CTC counts per ml of blood were: Pre-RT 20.2 (standard error (SE) 8.5), mid-RT 11.0 (SE 2.5), and post-RT 1.0 (SE 0.4). The difference in CTC counts from pre-RT to post-RT was statistically significant (p<0.03). Conclusions: We have successfully detected CTCs in patients undergoing definitive RT for localized prostate cancer with a novel CTC assay. CTC counts appear to decline after definitive radiotherapy. While these promising results may further aid research of CTCs in prostate cancer, the ultimate implications for subsequent patient decisions and management remain to be studied.