ERBB2 and breast cancer: Given the vital roles of cell-cycle pathway in the progression and therapeutic responsiveness of HR+/HER2– BC (3), we focused on the identified cell cycle–related proteins CDK4, protein phosphatase 2 catalytic subunit beta (PPP2CB), E2 transcription factor 5 (E2F5), tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein gamma (YWHAG), and transcription factor Dp-1 (TFDP1) for further investigation (Supplemental Figure 9A).