Effect of internal subtype on the efficacy of CDK4/6 inhibitor therapy in advanced HR+/HER2breast cancer: A review

The classification of breast cancer (BC) by immunohistochemical phenotypes is widely used in routine clinical practice. However, the genetic profile of the tumor does not always correspond to the pathomorphological one, which can significantly affect the prognosis and predict the effectiveness of therapy in BC. This literature review examines the effectiveness of endocrine therapy depending on the internal subtype of BC, and also presents data on the effectiveness of CDK4/6 inhibitors in these subgroups. It has been shown that during metastasis, the tumor acquires a more aggressive subtype (for example, it switches from luminal to HER2-E or basal-like), which can be stopped when using CDK4/6 inhibitors: the change of the internal subtype passes into a more favorable group.