Tumor cells circulate in the peripheral blood of all major carcinomas but not in healthy subjects or patients with non-malignant diseases.

9552 Background: The number of circulating tumor cells (CTC) in carcinoma patients may provide diagnostic and prognostic information to guide selection and monitor efficacy of therapies. This requires a standardized assay that is accurate and reproducible. Previous studies have demonstrated that CTC can be detected in peripheral blood of cancer patients, but a systematic survey of the prevalence of CTC in healthy subjects, patients with non-malignant diseases and a wide range of carcinomas is needed to establish a foundation for clinical implementation of this technology. METHODS We developed the CellSearch assay to accurately and reproducibly enumerate CTC in 7.5 ml of blood. The assay is based on immunomagnetic enrichment and fluorescent labeling of CTC followed by enumeration on a four color semi-automated fluorescence microscope. Blood from 145 healthy women, 199 women with non-malignant diseases and 1082 patients with a variety of metastatic carcinomas was tested for the presence of CTC. RESULTS Blood samples spiked with tumor cells were used to establish accuracy, reproducibility and linearity of the test. Recovery of spiked cells was ≥ 85% with a CV of 9.4% at a spike of 258 cells and 15.8% at a spike of 47 cells. The assay was linear over the tested range of 4 -1000 cells (r2=0.99). CTC in 344 healthy and non-malignant subjects were extremely rare with only one sample with > 1 cell/7.5 mL. In metastatic carcinoma patients CTC ranged from 0 to 3677 /7.5 mL (mean 32 ± 218). In 36% of the 1082 samples 2 or more CTC were present in 7.5 ml of blood. In 181 prostate cancer patients ≥2 CTC were detected in 57%, in 331 breast cancer patients 37%, in 47 ovarian cancers 36%, in 259 colorectal cancers 30%, and in 149 lung cancer patients 22%. CONCLUSIONS The CellSearch assay is a reliable highly sensitive assay that can be used to explore the clinical utility of CTC in carcinomas. CTC are present in various metastatic carcinomas with a wide range of frequencies. [Table: see text].