Real-time quantitative PCR determination of urokinase-type plasminogen activator receptor (uPAR) expression of isolated micrometastatic cells from bone marrow of breast cancer patients

Abstract

Disseminated tumor cells (DTC) in bone marrow are independently related to poor outcome in patients with breast cancer. Phenotypic characterization of DTC may be useful to improve evaluation of the metastasizing potential of DTC and also to more accurately target aggressive tumor cells. DTC were screened in bone marrow aspirates from breast cancer patients by immunocytochemistry with an anticytokeratin (anti-CK) antibody (A45B/B3). Because the cell permeabilization and fixation required for intracellular CK staining is deleterious for mRNA, we used microaspiration to isolate single tumor cells stained with a monoclonal antibody directed against a membrane epitope, epithelial cell adhesion molecule (EpCAM), in CK-positive cases. Urokinase-type plasminogen activator receptor (uPAR) was quantified by real-time quantitative RT-PCR. The SKBR3 human breast cancer cell line was used to calibrate RT-PCR. A linear relationship was observed between the cycle threshold (Ct) of uPAR and 18S gene expression and SKBR3 cells spiked (1, 3, 7, 10 and 20) in control patient bone marrow. EpCAM-positive cells were aspirated in 21 out of 25 bone marrow specimens from breast cancer patients with CK-positive cells and uPAR mRNA expression was determined in 16 cases. A high level of uPAR mRNA in DTC was detected in 8 out of 16 patients (50%) and was associated with a more aggressive primary tumor phenotype (estrogen receptor [ER]-negative, progesterone receptor [PR]-negative or HER2-positive) (p = 0.01). We demonstrated that real-time quantitative RT-PCR was reliably adapted to phenotype analysis of isolated micrometastatic cells. A larger study would be useful to confirm the importance of uPAR to define higher risk subgroups of breast cancer patients with micrometastatic disease. © 2004 Wiley-Liss, Inc.