Figure 1. . The primary tumors or metastasis are a composite of genetically heterogeneous cancer and stromal cells that can generate biomarkers detectable by liquid biopsy.

Tumors can shed circulating tumor cells into the bloodstream; apoptotic and necrotic process can instead originate cfDNA, released into the bloodstream. In addition, all cells from tumors can release exosomes, membrane-encapsulated vesicles containing different types of nucleic acids and proteins from the cells. All these elements (circulating tumor cells, cfDNA, exosomes) can be isolated from blood for molecular analysis.

cfDNA: Circulating-free DNA.