Circulating tumour cells as a window into lethality in prostate cancer.

Prostate cancer is characterized by multifocality, inter- and intra-patient tumour heterogeneity, and differences in risk of progression to metastatic disease, castration resistance and lethality, which can make prognosis challenging. Consequently, sampling methods that provide accurate insight into disease phenotype to facilitate risk-stratification of patients are crucial. The variable biology of prostate cancer seems to be recapitulated in the phenotypic heterogeneity of circulating tumour cells (CTCs). CTC sampling offers a liquid biopsy method to achieve minimally invasive longitudinal sampling for disease monitoring. CTC analysis has also offered a crucial insight into aggressive phenotypes, disease metastasis and treatment response, particularly in clinical trials. The clinical use of CTC count for prognosis in advanced prostate cancer has been approved by the FDA, but is not routinely used clinically, as these cells are technically challenging to isolate and analyse. However, methodological advances continue to improve CTC enrichment and profiling. Understanding the clinical utility of CTCs and future innovations is crucial to incorporating CTCs into the clinical management of prostate cancer.