Based on previous OPN studies and own findings regarding the role of ALCAM in breast cancer (Ihnen et al, 2008), we decided to evaluate the discriminative value of these genes in combination with HER2 and ESR1 in an effort to identify breast cancer subgroups, in which SPP1 and ALCAM are of particular relevance as we attributed to these genes a certain discriminative impact. The gene discussed is ESR1; the disease is breast carcinoma.