Likewise, the phase III PATINA study is evaluating the benefit of adding maintenance palbociclib to HER2-targeted therapy (trastuzumab ± pertuzumab) plus ET (AI or fulvestrant) in the 1L HER2+, ER+ mBC setting [93], while the phase II monarcHER study has demonstrated a significant PFS benefit with abemaciclib, trastuzumab, and ET versus trastuzumab plus chemotherapy (HR 0.67) in patients with HR+, HER2+ advanced BC who had received ≥ 2 HER2-targeted therapies for advanced disease [94]. Here, ESR1 is linked to breast cancer.