To investigate whether previously reported reduced levels of Nuc-pYStat5a/b during breast cancer progression could in part be caused by loss of Stat5a or Stat5b protein expression, a breast tissue progression array (Material I) that included normal breast, ductal carcinoma in situ (DCIS), invasive ductal carcinoma (IDC), and lymph node metastases, was stained for Stat5a or Stat5b with immunofluorescence labeling and quantified with AQUA (Figure 1). This evidence concerns the gene STAT5B and invasive ductal breast carcinoma.