As HS2ST1-dependent modification of Sdc-1 has recently been linked to breast cancer pathogenetic properties (Kang et al., 2020), we employed an siRNA depletion approach to downregulate the expression of Sdc-1 and Sdc-4 in sulfotransferase overexpressing MCF-7 cells, followed by qPCR analysis of HSPE, Sdc-1, Sdc4 and the notch ligand DLL1. Here, SDC4 is linked to breast cancer.