DLL1 and neoplasm: Indeed, BMSCs express Notch ligands, i.e., Jagged1, Jagged2 and Dll1, Dll3, and receptors, i.e., Notch1 and Notch2 (Bertrand et al., 2000; Nefedova et al., 2004; Xu et al., 2012a,b; Jitschin et al., 2015; Colombo et al., 2016; Sato et al., 2016), and many lines of evidence indicate that BMSC-derived Notch ligands may trigger Notch signaling in tumor cells inducing drug resistance.