Fig. 2.

The most influential events contributing to the causal relationship between CSCs and CTCs The fonts in black indicate events related to CSCs [1, 4, 32, 56, 57, 62–68]. The fonts in blue indicate events related to CTCs [9, 26, 28–34, 48, 54, 69–78]. And recent years, many evidence showed the inextricable connection between CSCs and CTCs, the expanded CTCs subsets are always used as a tool to reflect intrinsic characteristic of CSCs [25, 77, 78]. The abbreviations in Fig. 2: stem cells (SCs); mesenchymal stem cells (MSCs); serum-free medium (SFM); disseminated tumor cells (DTC); CTC-derived xenografts (CDX) [35–39, 43–48, 51, 52, 54]