Sensitive detection of circulating breast cancer cells by reverse-transcriptase polymerase chain reaction of maspin gene

Background: Maspin, a recently identified protein related to the family of serpins, is believed to play a role in human breast cancer. In an effort to improve the present methods of detection, we have developed a reverse-transcriptase polymerase chain reaction (RT-PCR) assay for maspin transcript to identify small numbers of mammary carcinoma cells in the peripheral blood and bone marrow of patients with breast cancer. Patients and methods: Five non-neoplastic mammary tissue samples, 13 breast cancer specimens as well as 17 peripheral blood and 4 bone marrow samples from normal subjects were screened for the presence of maspin mRNA by RT-PCR. The same assay was applied to peripheral blood or bone marrow samples obtained from 29 patients with stages I to IV breast cancer. Results: By RT-PCR it was possible to amplify maspin mRNA in all of the primary and metastatic breast cancer specimens, but in none of the normal hemopoietic samples from healthy donors. Thus, detection of maspin transcript in the peripheral blood or marrow of a patient known to have breast cancer is indicative of the presence of mammary carcinoma cells. In reconstitution experiments, maspin RT-PCR reliably detected 10 mammary carcinoma cells in 1 million normal peripheral-blood mononuclear cells (PBMCs). None of the 9 patients with stages I, II, or III breast cancer had maspin transcript in peripheral blood. Of note, 3 of 9 patients with stage TV breast cancer receiving systemic therapy at the time of sample collection, but only I of 11 patients with stage IV not receiving therapy, had detectable maspin transcript in peripheral blood. Moreover, 3 marrow specimens from stage TV patients tested positive by this assay. Conclusions: This pilot study suggests that maspin RT-PCR assay is a sensitive, specific and sufficiently rapid method for detection of small numbers of circulating cells and marrow micrometastases in breast cancer patients. The possibility of applying this assay in the detection of tumor cell contamination of both marrow and stem-cell apheresis harvests of breast cancer patients merits further investigation.