High frequency of HIF-1α overexpression in BRCA1 related breast cancer

Hypoxia is a hallmark of cancer. Hypoxia inducible factor-1α (HIF-1α) is the key regulator of the hypoxia response. HIF-1α is overexpressed during sporadic breast carcinogenesis and correlated with poor prognosis. Little is known on the role of HIF-1α in hereditary breast carcinogenesis. A recent study suggests a role for BRCA1 in HIF-1α regulation. We therefore examined the expression of HIF-1α in BRCA1 related breast cancers. By immunohistochemistry we studied expression of HIF-1α and some of its downstream targets in 30 hereditary invasive breast cancers in comparison with 200 sporadic controls. HIF-1α overexpression was significantly more frequent in BRCA1 related breast cancers (27/30, 90%) than in sporadic controls (88/200, 44%) (P < 0.0001). 19/30 (63%) of BRCA1 tumors showed perinecrotic (hypoxia induced) and 8/30 (27%) a diffuse HIF-1α overexpression pattern, the latter more likely related to genetic alterations in oncogenes and tumor suppressor genes. In contrast, sporadic breast cancer HIF-1 expressing tumors showed an inverse ratio of perinecrotic/diffuse expression (31 vs. 69%, P = 0.0002). Glut-1 and CAIX, downstream HIF1 targets, were expressed in 27/30 (90%) and 15/21 (71%) of hereditary cases versus 54/183 (29%) and 24/183 (13%) in sporadic cases. p300 levels, necessary for HIF-1 downstream activation, were significantly higher in hereditary cases (20/21, 95%) compared to sporadic cases (91/183, 50%, P = 0.0001). In conclusion, in BRCA1 germline mutation related breast cancer, functional HIF-1α overexpression is seen at a much higher frequency than in sporadic breast cancer, mostly hypoxia induced. This points to an important role of hypoxia and its key regulator HIF-1α in hereditary breast carcinogenesis.