Figure 1.

Intratumour heterogeneity through space and time. In a tumour, genetic and epigenetic alterations may result from the emergence of a group of self-renewing CSCs. Through microenvironment interventions, including the immune response and drug treatment, some CSCs are inhibited. However, some genetic alterations occur in specific CSCs, helping the CSC to gain the ability to survive treatment, a process that is known as clonal evolution. After several cycles of intervention, the surviving CTC is capable of tumour progression and metastasis, affecting the patient's survival. CSC, cancer stem cell; CTC, circulating tumour cell.