Migrating and circulating breast carcinoma cells are within active phases of the cell cycle

The emergence of blood-borne epithelial-derived tumour cells in breast cancer patients is generally supposed to be an indicator of cancer cell spread but only a very small percentage of these cells ultimately initiate metastases. In this study, we investigated the presence of the cell cycle marker Ki-67 in mammary tumour cells isolated from patients' blood and SKBR3 breast carcinoma cells by confocal laser scanning microscopy. We also compared the immunostaining patterns for Ki-67 of blood-borne tumour cells from the patients with actively migrating cells within a collagen matrix. Both circulating tumour cells and migrating SKBR3 cells were found to be in G1- or S-phase. These findings will have impact on adjuvant chemotherapy as circulating tumour cells that are within the active part of the cell cycle are highly susceptible to chemotherapeutic agents and therefore can be killed while they migrate to distant organs to build a metastasis.