Identification and quantitation of circulating tumor cells

Circulating tumor cells (CTCs) are shed from the primary tumor into the circulatory system and act as seeds that initiate cancer metastasis to distant sites. CTC enumeration has been shown to have a significant prognostic value as a surrogate marker in various cancers. The widespread clinical utility of CTC tests, however, is still limited due to the inherent rarity and heterogeneity of CTCs, which necessitate robust techniques for their efficient enrichment and detection. Significant recent advances have resulted in technologies with the ability to improve yield and purity of CTC enrichment as well as detection sensitivity. Current efforts are largely focused on the translation and standardization of assays to fully realize the clinical utility of CTCs. In this review, we aim to provide a comprehensive overview of CTC enrichment and detection techniques with an emphasis on novel approaches for rapid quantification of CTCs.