To further evaluate potential mechanisms by which SDC3 influences cell viability, cell-cycle phases, stemness-associated factors, and cell migration mainly in MDA-MB-231 and in MCF-7 breast cancer cells, we examined the effect of SDC3 downregulation on the potential activation of Src proto-oncogene tyrosine-protein kinase (pSRC), as well as on the expression of its total form (SRC). The gene discussed is SDC3; the disease is breast carcinoma.