PSMG4 and breast cancer: The proteasome assembly chaperone (<i>PSMG</i>) gene family (comprised of <i>PSMG1</i>, <i>PSMG2</i>, <i>PSMG3</i>, and <i>PSMG4</i>) plays a critical role in proteasome biogenesis; however, its involvement in breast cancer remains poorly understood.