The presence of low oxygen (hypoxia) in tumors, as detected by the immunohistochemical staining of tumor sections for established hypoxic markers such as carbonic anhydrase IX (CAIX), correlates with a poorer clinical outcome in breast cancer 3,4 Thus incorporating features such as hypoxia into screening models may enhance our capacity to discover novel drug targets that will be more efficacious in vivo. This evidence concerns the gene CA9 and breast carcinoma.