The presence of circulating tumor cells (CTC) in the peripheral blood of cancer patients has been described for various solid tumors and their clinical relevance has been shown. CTC detection based on the analysis of epithelial antigens might be hampered by the genetic heterogeneity of the primary tumor and loss of epithelial antigens. Therefore, we aimed to identify new gene markers for the PCR-based detection of CTC in female cancer patients.

Gene expression of 38 cancer cell lines (breast, ovarian, cervical and endometrial) and of 10 peripheral blood mononuclear cell (PBMC) samples from healthy female donors was measured using microarray technology (Applied Biosystems). Differentially expressed genes were identified using the maxT test and the 50% one-sided trimmed maxT-test. After confirming the microarray results, we analyzed the expression of 93 gene targets with RT-qPCR using TaqMan Low Density Arrays (Applied Biosystems) in tumor tissues of 126 patients with primary breast, ovarian or endometrial cancer, and in 151 blood samples. The blood was taken from 26 healthy women, from 94 patients with breast, ovarian, cervical or endometrial cancer at initial diagnosis , and from 31 patients with recurrent breast cancer. Likewise, hMAM and EpCAM gene expression was analyzed in the blood of breast and ovarian cancer patients. For each gene, a cut-off threshold value was set at three standard deviations from the mean expression level of the healthy controls to identify potential markers for CTC detection.

In the blood samples of breast cancer patients, six genes were over-expressed in 81% of patients with recurrent disease and in 29% of patients at initial diagnosis. EpCAM gene expression was detected in 19% and 5% of the breast cancer patients, respectively, whereas hMAM gene expression was observed in patient with recurrent disease (39%) only. Multimarker analysis using the new six gene panel positively identified 44% of the cervical, 64% of the endometrial and 19% of the ovarian cancer patients.

The panel of six genes was found superior to EpCAM and hMAM for the detection of circulating tumor cells in the blood of breast cancer, and they may serve as potential markers for CTC derived from endometrial, cervical, and ovarian cancers.

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