Fig. 2: Components of liquid biopsy in GC.

CTCs, ctDNA, and exosomes were discovered in the peripheral blood. CTCs and ctDNA are important ingredients that are usually regarded as the foundations of liquid biopsy. ctDNA is formed from apoptotic and necrotic tumor cells, which release fragmented DNA into the bloodstream and possess genetic aberration from original tumor cells. CTCs are cancer cells that spontaneously shed from primary or metastatic tumors and circulate in the circulation. They are tumor “seeds” and can result in recurrence by hepatic metastasis, lymphatic metastasis, and angiogenesis.