Molecular detection of HER2 mRNA-positive cells in the peripheral blood of patients with operable breast cancer

Abstract

668 Background: To evaluate whether the detection of peripheral blood (PB) HER2 mRNA+ positive cells in patients with breast cancer could be another marker of the micrometastatic disease. Methods: The sensitivity and specificity of HER2 mRNA detection by nested RT-PCR were investigated using MCF-7 and ARH-77 cells as well as blood from healthy women and patients with colorectal, early and metastatic breast cancer. PB from 216 patients with operable breast cancer, obtained before initiation of any adjuvant therapy, was tested for the presence of HER2 mRNA+ positive cells. Results: In dilution experiments the nested RT-PCR assay for HER2 mRNA was capable of detecting up to 105 MCF-7 tumor cells in 105 normal peripheral blood mononuclear cells; no signal was detected with the HER2- ARH-77 cells. No HER2 mRNA+ cells could be detected in the peripheral blood of 31 healthy women, as well as the peripheral blood and the bone marrow of 20 patients with colorectal cancer. Detection rates for HER2 mRNA+ cells in the bone marrow/blood of patients with early or metastatic breast cancer were 36.4%/23.8% and 35.5%/18%, respectively. Double immunostaining with a pan-keratin and a HER2 monoclonal antibody and confocal microscopy analysis revealed co-expression on PB cells in 5 (38.5%) of 13 patients. In addition, FISH analysis of PB tumor cells from 5 patients demonstrated HER2 gene amplification in all patients. Finally, aneusomy cells could be detected by LSI 1, CEP 8, CEP 11 and CEP 11 with chromosomal gain or loss in 2 of the patients. Conclusions: The results demonstrate that occult tumor cells expressing HER2 mRNA could be detected in the peripheral blood of patients with operable breast cancer; these cells are not always CK+ indicating that HER2 mRNA detection may represent another marker of the micrometastatic disease. No significant financial relationships to disclose.