Liquid Biopsies: As an Emerging Tool in Cancer Diagnosis and Monitoring Therapies in Metastasis

Despite the availability of advanced diagnosis and treatment methods, cancer is still a leading cause of morbidity. The most readily and routinely available method for cancer diagnosis is tissue biopsy. Tissue biopsies are generally based on molecular profiling of primary tumors, which can change during the metastasis stage. Therefore, it’s unable to give sufficient information about the tumor. These problems can be overcome by liquid biopsies which is considered as fast, non-invasive, and more sensitive method for cancer diagnosis. It also has applications in early diagnosis and real-time monitoring of tumor prognosis and development. This can be achieved by molecular profiling of circulating tumor cells (CTCs), cell-free DNA (cfDNA), exosomes, microRNA (miRNA), and tumor-educated platelets (TEPs) from biological fluids which are considered as biomarkers. The expression of these biomarkers gives an entire snapshot of both the primary and metastasis stages of cancer. It is very useful to determine different stages of cancer and to modify treatment strategies based on treatment response. Therefore, it opens up an opportunity to use liquid biopsies in the area of precision medicine. This review summarizes in-depth information on liquid biopsies, cancer metastasis, various methods in liquid biopsies, biomarkers such as CTCs, cfDNA, miRNA, exosomes, TEPs, and the role of these biomarkers in monitoring therapy.