Early exploration of circulating tumor cells (CTC) as a predictive biomarker for cancer treatment response

A50

The presence of CTC has been associated with a number of human carcinomas. We have established a method for detecting CTC in 1-2 mL of blood to explore CTC in cancer patients. Briefly, leukocytes and platelets are depleted from blood with an antibody cocktail (CD45/CD36/CD66b). The unbound, negatively selected cells are cytospun onto a slide, stained with an epithelial specific antibody cocktail and analyzed using automated microscopy. CTC can be detected in the blood of patients with a variety of solid tumors. A longitudinal analysis was performed on a subset of patients from M02-428, an ABT-510 Phase II renal cancer trial (N=33). We observed a range of CTC concentrations at baseline (0 to 43 CTC/mL). Following one cycle of ABT-510 treatment, the CTC frequently detected at baseline, became undetectable in the blood of most patients.An advance in the field of CTC analysis was the FDA approval of a CTC detection method for monitoring the status of metastatic breast cancer, using a fully automated CellSearch System, developed by Immunicon. Based on the published reports using this technology and our internal CTC assessment, we have initiated in-house validation tests to assess the CTC detection and examined CTC from prostate, colon and head/neck cancer patients. The CTC detected range in these patient specimens ranged from 0 to 2187 (N=98) per 7.5 ml of whole blood, with > 5 CTC in 36 specimens and < 5 CTC in 62 specimens. Detection and enumeration of CTC may bring new insight to understanding metastatic processes and may provide a sensitive index of tumor response to therapy.