This study enrolled men with prostate cancer who had failed hormone therapy (as shown by rising prostate-specific antigen [PSA] levels) and who were about to start a new line of chemotherapy. Blood was drawn prior to the patient receiving chemotherapy and then monthly thereafter for up to 18 months or until disease progression, whichever occurred first. The blood was tested to find circulating tumor cells (CTC) and to count them. The circulating tumor cell levels were studied in relation to the patient's overall survival. Serum was also collected for PSA testing, and additional blood samples were drawn to test for circulating endothelial cells and RNA was isolated for future gene expression testing.