Fig. 1.

Advantages and disadvantages of circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) in metastatic colorectal cancer (mCRC). Collection of CTCs is mainly impaired by their low abundance in plasma (median 2 CTCs/7.5 mL of peripheral blood in mCRC). Furthermore, high heterogeneity of cell surface expression and loss of epithelial markers (due to epithelial-mesenchymal transition [EMT]) also contribute to complexity in CTC isolation; their use allows cell culturing and xenografting, hence bridging the clinical and preclinical scenarios. On the contrary, ctDNA is easily detectable in peripheral blood and its feasibility allows intensive clonal tracking and monitoring of emerging resistance mechanisms during active treatment in mCRC; however, a low frequency of certain genomic aberrations and interference of non-neoplastic clonal expansion may compromise sensitivity and specificity. Created with smart.servier.com