Using a monoclonal antibody, we have shown in formalin-fixed, paraffin-embedded, breast tissue ranging from simple hyperplasia to invasive carcinoma that a direct correlation exists between abnormalities in breast epithelial cells and reduction in STAT5a expression, with STAT5a expression being decreased in ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (Bratthauer et al. 2006). The gene discussed is STAT5A; the disease is invasive ductal breast carcinoma.