Metastatic breast cancer and circulating tumour cells

Circulating tumour cells - often referred to as a 'liquid biopsy' for cancer - can be found in a large proportion of patients with breast cancer that has spread to other organs. Changes in circulating tumour cell levels in metastatic breast cancer patients receiving chemotherapy have been shown to correlate with survival. Consequently, they have been shown to be an independently important way of predicting both the course of the metastatic disease, which will ultimately prove to be fatal, and the magnitude of response to systemic therapy. Circulating tumour cell research will not only elucidate the metastatic process but will also provide a platform for development of new cancer treatment regimens and drug targets. In this article, we will show how circulating tumour cell analysis is currently used in clinical practice, in clinical trials and the challenges that remain both in detecting these rare cells in the blood and in unravelling their molecular signatures, which may differ considerably from the primary cancer. As the isolation and characterisation of circulating tumour cells steadily improves, new metastatic breast cancer treatments will be developed, old regimes refined and patients will ultimately benefit.