Results of telomerase activity measurements from live circulating tumor cells captured on a slot microfilter in a phase III SWOG-coordinated prostate cancer trial (S0421).

Abstract

4663 Background: Analysis of circulating tumor cells (CTC) is a promising biomarker strategy in advanced prostate cancer, and telomerase activity (TA) is a recognized cancer marker. To test whether CTC TA is prognostic for survival (OS), we developed a novel Parylene-C slot microfilter capable of capturing live CTC and used it to measure CTC TA as part of a Phase III SWOG-coordinated therapeutic trial in metastatic castration resistant prostate cancer (S0421). Methods: Blood samples were drawn into EDTA tubes and shipped overnight to a central processing site. After Ficoll centrifugation, low constant pressure was used to pass the mononuclear cell layer through two slot microfilters in series as published previously (filter1 captures CTC + background white blood cells; filter2 captures only background white blood cells). Filter-trapped cells were lysed in CHAPS buffer and assayed for TA using qPCR-based telomeric repeat amplification. In parallel, CTC were enumerated using CellSearch (J&J). Cox regression was used to evaluate the association between baseline (pre-treatment) TA and OS overall, and within subgroups characterized by good prognosis (<5) vs. poor prognosis (>=5) baseline CTC counts. CART regression was used to explore potential prognostic subgroups based on baseline PSA, CTC, and TA cutpoints. Results: Samples were obtained from 263 patients. While no association was observed between TA and OS overall, in patients with baseline CTC >=5 (108 of 263 or 41% of patients), TAfilter2 – TAfilter1 representing high CTC TA relative to background blood cells was associated with a hazard ratio (HR) of 1.14 (95% CI 1.05-1.23, p<0.001) for OS after adjusting for risk factors and remained significant when also adjusting for CTC: HR 1.14 (95% CI 1.04-1.23; p=0.005). Exploratory CART regression assessing baseline PSA, CTC, and TA identified risk groups based only on CTC and TA values. Conclusions: Baseline TA from CTC live-captured on a new slot microfilter is the first CTC biomarker shown to be prognostic of OS in men with CTC counts >=5 in a prospective clinical trial. CTC TA may be useful for further identifying prognostic groups in this population.