Background: Initial validation of a seminested reverse transcription-polymerase chain reaction (RT-PCR) assay for HER2/neu for use in detecting circulating tumor cells in the peripheral blood or bone marrow of breast cancer patients is described. RT-PCR assays for other epithelial markers, including the cytokeratins and carcinoembryonic antigen frequently lack specificity, sensitivity, or both. Thus, there is a need for an assay that is both sensitive and specific to be used to monitor breast cancer patients for micrometastatic or minimal residual disease.
Method and results: Assay conditions were optimized using the MCF7 breast cancer cell line and the Raji B-cell lymphoma cell line. The assay can detect as little as 3 mg of MCF7 RNA within a background of 3 mg of Raji RNA. The assay was positive in 12 of 12 breast tumors. None of the 33 peripheral blood or stem cell samples form patients without evidence of breast cancer were positive. Peripheral blood from 17 breast cancer patients was collected immediately before surgery and evaluated. The assay was positive in five of six patients with Stage II, four of eight patients with Stage I and one of three patients with Stage 0 disease.
Conclusions: The seminested HER2/neu RT-PCR assay compares favorably with RT-PCR assays for other epithelial cell markers in terms of both sensitivity and specificity as a method to detect disseminated breast cancer cells. In breast cancer patients, the higher the disease stage, the more frequently was the assay positive.