An RT-PCR assay to monitor circulating free DNA (cfDNA) in castrate resistant prostate cancer (CRPC).

Abstract

346 Background: Circulating-free DNA (cfDNA) is elevated in many forms of advanced cancer. We used an RT PCR assay for a highly repetitive DNA element (long-interspersed nuclear element-1; LINE1) to assess cfDNA in patients with CRPC. Methods: Plasma was collected from subjects with metastatic CRPC prior to a change in therapy. DNA was extracted and analyzed with an RT-PCR assay targeting a 297-bp LINE1 amplicon using absolute quantification. Leukocyte DNA and plasma from normal males were used as controls. Serial plasma samples were collected to monitor changes in cfDNA relative to treatment interventions. Results: cfDNA was analyzed at baseline in 54 samples categorized according to treatment context as: chemotherapy-naïve, docetaxel, or post-docetaxel (Table, summarized as means ± SD). While LINE1 was elevated in most patients relative to normal controls, no significant differences were noted across patient groups. No correlation was found between LINE1 and other clinical variables. Longitudinal sampling demonstrated concordant changes in LINE1 and PSA in most subjects, while a discordant pattern was noted in others. Conclusions: The LINE1 RT-PCR assay can be used to monitor cfDNA levels in patients with CRPC and may provide independent information to standard clinical assessments in order to monitor tumor composition and therapeutic response. [Table: see text]