To this end, we set out to compare expression levels of five tumor specific membrane bound candidate imaging [8–11] and drug targets (Claudin-4, the Epidermal Growth Factor Receptor (EGFR), Carbonic Anhydrase IX (CAIX), the Glucose Transporter 1 (GLUT-1) and the Insulin Growth Factor Receptor 1 (IGF1R) in primary breast cancers and their distant metastases, and hypothesised how this would impact molecular imaging and targeted therapy. This evidence concerns the gene CLDN4 and breast cancer.