JAG1 and neoplasm: Interestingly, Jagged1, a Notch1 ligand, is not only expressed in tumour cells but also in bystander cells neighbouring tumour cells that lead to activated NOTCH1 through homotypic or heterotypic cell–cell interactions, resulting in activated NOTCH1 and a dramatic increase in the growth of tumour cells, preventing cell apoptosis and affecting the tumour microenvironment [71,72].