PSMB9 and breast cancer: Moreover, PARP9 expression positively correlates with metastasis of axillary lymph node and is negatively associated with ER expression [102], as well as PSMB8 and PSMB9 and immunoproteasomes, which induce tumor angiogenesis via VEGF-A and are overexpressed in most cancers, including BC [73,74].