Clinical trials have demonstrated that palbociclib significantly increases the progression-free survival (PFS) of patients with advanced ER+ and HER2-negative (HER2−) breast cancer, not only in the first-line setting in combination with letrozole, but also in the second-line setting in combination with fulvestrant after disease progression following endocrine therapy [7,8,9]. Here, ERBB2 is linked to breast carcinoma.