While MDA-MB-435 S cells expressing Sulfatase 2 can represent a valid model to study the effect of endogenous Sulfatase 2 in breast cancer, we have chosen MDA-MB-231 cells as a model for our study because they have undetectable levels of endogenously produced human Sulfatase 1 or Sulfatase 2 as analyzed by RT-PCR (Fig. 1A). The gene discussed is SULF1; the disease is breast cancer.