This was achieved through the hybridisation of a sample of UHRR to a single array on each chip along with duplicate preparations of cRNA from fresh frozen breast tumour samples that formed part of a recent clinical study (Sabine VS, Sims AH, Macaskill EJ, Renshaw L, Thomas JS, Dixon JM, Bartlett JMS: Gene Expression Profiling of Response to mTOR Inhibitor Everolimus in Pre-operatively Treated Post-menopausal Women with Estrogen Receptor-Positive Breast Cancer, Submitted). The gene discussed is ESR1; the disease is breast cancer.