Using a stepwise approach combining genome-wide expression profiling and TaqMan® based RT-qPCR we identified six genes (CCNE2, DKFZp762E1312, EMP2, MAL2, PPIC, and SLC6A8) as potential markers for the detection of circulating tumor cells in the peripheral blood of patients with breast cancer and gynecological malignancies. Here, SLC6A8 is linked to breast cancer.