Human mammaglobin RT-PCR assay for detection of occult breast cancer cells in hemotapoietic products

Background: The aim of this study was: (i) to evaluate the sensitivity and specificity of mammaglobin as a reverse transcriptase polymerase chain reaction (RT-PCR) marker of breast cancer cells; (ii) to determine the incidence of tumor cell contamination of hematopoietic samples from patients with breast cancer. Materials and methods: A nested RT-PCR assay for mammaglobin was developed. Sensitivity was determined by serial dilution assays with breast cancer cell lines, human breast cancers and normal breast tissue. Specificity was evaluated in hematopoietic samples from healthy volunteers and patients with hematological malignancies or solid tumors other than breast cancer. Results: The mammaglobin transcript was detected in all 15 breast cancers, one benign breast tumor and five normal breast tissues studied, as well as in three breast cancer cell lines, in dilutions as low as 10^-8. The transcript was not detected in any of 47 peripheral blood samples, 15 bone marrow aspirates and 28 peripheral blood progenitor cell samples from the three control populations. Mammaglobin mRNA was detected in 19 of 78 peripheral blood samples from patients with breast cancer starting systemic chemotherapy, as well as in five of 30 repeat samples collected before the fourth cycle of treatment. The transcript was also present in six of seven bone marrow aspirates from patients with metastatic disease, two of five with loco-regional disease, but not in the aspirate of two patients with thrombocytopenia and a previous history of breast cancer. Conclusions: Human mammaglobin mRNA is a sensitive and specific marker of breast cancer cells and should be further studied as a molecular marker of tumor cell contamination of hematopoietic tissues.