CA9 and invasive breast carcinoma: A subset of invasive breast cancer cases (n=150) was additionally analysed for protein level expression of the hypoxia-inducible (transcription) factors 1α and 2α (HIF-1α, HIF-2α), which are generally considered as the key regulators of the hypoxic response in cells and tissues, and their down stream targets GLUT1 and CAIX.