ABSTRACT
Circulating tumour cells (CTCs) are emerging as important prognostic markers and have potential clinical utility as tumour biomarkers for targeted cancer therapy. Although CTCs were proposed more than 100 years ago as potential precursors that may form metastatic lesions, formal evidence that CTCs are indeed capable of initiating metastases is limited. Moreover, the process of CTCs shedding into the circulation, relocating to distant organ sites and initiating metastatic foci is complex and intrinsically inefficient. To partially explain the metastatic process, the concepts of CTCs as metastatic precursors or pre-metastatic conditioners have been proposed; however, it is questionable as to whether these are both variable pathways to metastasis or just markers of metastatic burden. This review explores the evidence for CTCs in the initiation and progression of metastatic cancer and the data supporting these different concepts in an attempt to better understand the role of CTCs in metastasis. A greater understanding of the metastatic potential of CTCs will open new avenues for therapeutic interventions in the future.
Subject(s)
Neoplasms/pathology , Neoplastic Cells, Circulating , Animals , Humans , Neoplasm Metastasis , Neoplasms/genetics , Neoplasms/metabolism , Neoplasms/mortality , Tumor MicroenvironmentABSTRACT
The detection of circulating tumour cells or circulating free tumour nucleic acids can potentially guide treatment and inform prognosis in colorectal cancer using minimally invasive "liquid biopsies". Current literature supports the notion that high circulating tumour cell counts or presence of tumour nucleic acid correlate with inferior clinical outcomes for patients, but they are not yet part of routine clinical care. Future research evolves around the examination of the molecular phenotype of circulating tumour cells. The key unanswered areas include differentiating between circulating tumour cell presence and their proliferative capacity and dormancy, identifying tumour heterogeneity and understanding the epithelial-mesenchymal transition.
