Early cancer detection and personalized therapy have proven vital for patient diagnostics, prognostic, and long-term survival. Identifying and characterizing tumor cells provide critical information to diagnose, monitor, and potentially interfere with the metastatic process. A solid tumor biopsy, established as a standard clinical application, is invasive, expensive, time-consuming, and often perplexed by tumor heterogeneity. Liquid biopsies are relatively non-invasive and can be collected and tested repeatedly, with the testing including the latest DNA and RNA sequencing analyses. CTCs could even provide global information on metastatic risk, disease progression, and treatment effectiveness.