Additionally, high levels of CDK4 mRNA are related to the response to palbociclib plus hormonal therapy, while the increase of TK1 and CDK9 mRNA copies is related to clinical resistance.[213] Yang et al. suggest that the levels of glutathione S‐transferase P1 (GSTP1), a phase II metabolic enzyme, in serum exosomes of breast cancer patients who have received anthracycline/taxane‐based neoadjuvant chemotherapy are higher in the progressive/stable disease group than those in the partial/complete response group, suggesting the predictive role of GSTP1‐containing exosomes.[214]. This evidence concerns the gene GSTP1 and breast cancer.