To test this hypothesis, in this work, we analyzed for the first time the effect of knocking down of Sdc-1 (Sdc-1 KD) over HA expression and function in widely used, prototypic breast cancer cell lines with different levels of aggressiveness, MCF-7 as a representative luminal cell line, and MDA-MB-231 as a representative triple-negative/basal cell line. The gene discussed is SDC1; the disease is breast cancer.