On the other hand, as the expression of STAT5A, p-STAT5 and Notch3 (N3ICD) were highest in MCF-7, a luminal subtype breast cancer cell line and lowest in BT549, a TNBC cell line, the in vitro experiments were conducted in these two subtype breast cancer cell lines to confirm the regulation of Notch3 on the expression of STAT5A and its activation as well. The gene discussed is STAT5B; the disease is breast cancer.