Detection of metastatic breast cancer by β-hCG polymerase chain reaction

Reverse transcriptase-polymerase chain reaction (RT-PCR) for detection of occult malignancies in breast cancer patients is evolving as a useful diagnostic tool. However, no reliable molecular mRNA markers are available. We developed an RT-PCR plus Southern blot assay using β-hCG (β-subunit of human chorionic gonadotropin) gene expression as a tumor marker for detection of breast malignancies metastatic to tumor-draining lymph nodes and blood. Breast carcinoma cell lines, primary breast malignancies and human placenta were used as positive controls for establishing the β-hCG RT-PCR assay. Peripheral blood leukocytes (PBL) from normal volunteer donors, normal breast tissue and lymph nodes from cancer-free patients were used as negative controls. β-hCG RT-PCR was used to assess tumor cell presence in PBL and tumor-draining axillary nodes from patients with AJCC stage I-IV breast cancer. The assay sensitivity and specificity were enhanced by restriction endonuclease digestion of an Sty I site of the RT-PCR cDNA product followed by Southern blot analysis. β-hCG mRNA was expressed in all breast cancer cell lines and 80% of primary breast cancers; it was not expressed in negative controls. The assay reliably detected one cancer cell in > 10⁷ PBL, with a sensitivity of 10^-5 μg RNA. Eighty percent of PBL and 61% of tumor-draining axillary nodes from breast cancer patients expressed β-hCG mRNA. The assay is a sensitive and specific method of identifying breast cancer cells in breast tissues, lymph nodes and blood.