SDC1 and breast carcinoma: CD38 is a glycoprotein found almost ubiquitously on the surface of multiple immune cells, including PCs, activated B cells, GC B cells, T cells, NK cells, macrophages and DCs [93,94,95,96,97], whereas CD138, also known as syndecan-1, is an integral membrane proteoglycan [98] expressed not only in PCs but also in epithelial and stromal cells [99], including even breast carcinoma cells [32,100].