Immunohistochemical staining on consecutive sections for (a), (c) and (e) CD31 and (b), (d) and (f) hypoxia-inducible factor 1 alpha (hif-1α) in human breast cancer. Classical hif-1α expression (b) at the border of a necrotic region or (c) and (d) at a distance of 100–150 μm from blood vessels. (e) and (f) Occasional diffuse hif-1α staining throughout the entire tumor unpersuaded by the presence of capillary vessels. Asterisk denotes necrotic area. Arrowheads point to capillaries.