Assessment of the variability of and effect of hormone therapy on circulating tumor cell numbers and androgen receptor expression in patients with prostate cancer.

e15141 Background: In prostate cancer (PC) CTC number and character may offer a means of assessing disease load and target engagement. However, capture platforms differ, presenting challenges to enumeration and molecular characterisation. We report the findings of a pilot study assessing the intra- and inter-patient variability of 2 different platforms, and the feasibility of measuring CTC-androgen receptor (AR) expression by immunohistochemistry (IHC) in a single platform. Methods: Following ethical approval, 4 PC cohorts (n = 12, 12, 10, and 6 respectively) were recruited; #1 localised, no hormonal therapy; #2 and #3: castrate-resistant, receiving LHRHa or LHRHa and bicalutamide, respectively; #4: newly diagnosed locally advanced, no hormonal therapy. Blood (2 x 10 mL, 2 visits #1-3; 2 x 10 mL,1 visit #4) was taken and CTCs isolated using either the Cell Search CTC Test (Veridex) or Isolation by Size of Epithelial Cells Technique (ISET) for enumeration, and ISET for AR expression (H-score [(% 1*1+) + (%...