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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. © 1996 Wiley‐Liss, Inc.