Blood contains many types of biological materials such as circulating cells, platelets, extracellular vesicles, mRNA, miRNA, protein, and cfDNA (Sollott,2017). In the blood of cancer patients, some of the cfDNA (circulating tumor DNA (ctDNA)) is released by tumor cells via apoptosis, necrosis, or active release (Stroun et al., 2001). Tumor-specific mutations in the ctDNA sequence can be used as a new type of biomarker. The test using this ctDNA sequence in the body is called a liquid biopsy.
Compared to traditional cancer diagnosis using tissue biopsy, liquid biopsy is more feasible, noninvasive, and more comprehensive than tissue biopsy to assess tumor heterogeneity. Because different tissue/organ cancers release ctDNA into the blood at different rates (Siena et al., 2018). However, these variants, which are found at very low rates in circulation, cannot always be detected by this method. In this sense, evaluating the molecular genetic results of peripheral blood together with solid tissue provides serious advantages.
Liquid biopsy is a powerful technique that can be applied at different cancer screening and treatment stages. It can be used in many types of cancer, such as lung cancer, breast cancer, colon cancer, and stomach cancer. It can be used for early diagnosis and better intervention among asymptomatic cancer populations (Lindforss et al., 2005). After cancer diagnosis, it enables the tumor-specific molecular profile of patients to guide targeted therapy for precision medicine. The possibility of recurrence after cancer treatment, even after successful treatment, is still a significant threat to many cancer patients. Since it is not always possible to detect in a timely manner using imaging or tissue biopsy (Reinert et al., 2016), it can be detected earlier with the liquid biopsy method.