Breast cancer is one of the most common malignancies in women. About 70% of patients are estrogen receptor (ER) and/or progesterone receptor (PR) positive. Endocrine therapy is one of the main treatments for hormone receptor (HR) positive breast cancer. In recent decades

endocrine therapy drugs have been continuously innovated and applied in clinical practice

the risk of recurrence/metastasis of breast cancer patients has been significantly reduced

and the prognosis has been greatly improved. Among them

aromatase inhibitors (AIs) play an important role in endocrine therapy for breast cancer. However

a large number of patients develop either primary or secondary endocrine therapy drug resistance. Therefore

it is very important to overcome endocrine therapy drug resistance to further improve clinical efficacy. This article reviewed the mechanisms and the latest research progress of drug resistance in HR-positive breast cancer after prior AI therapy from the aspects of genetics

epigenetics and intracellular signal transduction pathways

so as to provide some guidance for clinical diagnosis

treatment and scientific research.