Analyzing the expression in 239 paraffin-fixed patient breast tissue sections (104 invasive breast cancer sections with corresponding metastatic lymph node section and progesterone receptor-, estrogen receptor- and Her2neu expression, BR20837; 17 invasive ductal,1 medullary carcinoma and 6 normal breast tissue sections, BR248a; 2 invasive ductal carcinomas, 1 invasive lobular carcinoma and 2 normal breast tissue section, T087a). The gene discussed is ESR1; the disease is invasive breast carcinoma.