Shaffer DR et al. (2007) Circulating tumor cell analysis in patients with progressive castration-resistant prostate cancer. Clin Cancer Res 13: 2023–2029

Factors that contribute to prostate cancer growth and survival vary over time, which might mean that drug therapies lose effectiveness in a given individual. Assessment of the molecular profile of tumors through analysis of circulating tumor cells (CTCs) might help to target therapy. Shaffer and colleagues collected peripheral blood from patients with advanced prostate cancer and used immunomagnetic-capture technology to isolate and analyze CTCs.

Around 7.5 ml of blood was collected from each of 63 patients with metastatic prostate cancer and from 17 controls without cancer at one US center. CTCs were captured with antibodies to the epithelial cell adhesion molecule and underwent immunofluorescent, Papanicolau staining and fluorescence in situ hybridization. To assess whether cell counts changed over time, additional samples were taken within 24 h of the first sample and at 72 h or at 96 h.

The mean CTC count in patients with prostate cancer was 16 cells/7.5 ml blood (range 0–847 cells). Subsequent CTC counts did not differ from those of the first samples. Cells expressed cytokeratin AE1/AE3 and α-methyl CoA racemase. There was marked amplification of the androgen receptor locus in five patients with CTC counts of 50 or more. Four of these patients, and an additional two, showed signals of tetraploidy. No amplification of ERBB2 (HER2) was observed. The proportion of CTCs positive for EGFR ranged from 0% to 100% (median 56%).

The authors hope that ongoing prospective studies will validate the markers identified, which might in turn improve clinical management of patients.