Moreover, palbociclib demonstrated a synergistic effect when combined with trastuzumab in HER2-positive cell lines.[8] El Chaarani et al[9] investigated the addition of palbociclib to a combination of trastuzumab and pertuzumab in HER2-positive breast cancer cell lines and confirmed that palbociclib was effective in both resistant and nonresistant HER2-positive cells. This evidence concerns the gene ERBB2 and breast cancer.