Biology and clinical relevance of circulating tumour cells

Assessment of circulating tumour cells (CTCs) provides a novel approach to interrogating cancer biology and CTCs have potential to serve as clinically useful biomarkers. The presence of CTCs and their role in metastasis has long been hypothesised but it is only in recent years that technology has allowed reliable isolation of CTCs leading to a renewed interest in this area. CTCs are commonly found in the blood of patients with cancer but are rare in the blood of healthy volunteers’ and those with benign disease (1). As technologies for CTC isolation have evolved, so too has the ability to characterise CTCs at the molecular level, paving the way to better understand metastasis biology; and CTCs could serve as a minimally invasive ‘liquid biopsy’ for longitudinal monitoring throughout the course of a patient’s treatment. This approach could be particularly useful to describe tumour evolution, assess pharmacodynamic biomarkers for drug development and reveal inherent or acquired treatment resistant mechanisms in a way that has been historically challenging due to difficulties in obtaining successive biopsies in lung cancer patients.