Hormone therapy is a major therapy for hormone receptor-positive breast cancer that improves survival. However, despite these hormone treatments, there are de novo or acquired resistance of breast cancer. Many studies revealed these resistance mechanisms, which are related to hormonal receptors including low expression or mutation of estrogen receptor alpha(ERα), co-factors and progesterone receptor, and with activation of growth signaling pathways such as PIK3A/Akt/mTOR pathway or cell cycle pathway. To overcome endocrine resistance based on these mechanisms, there have been many efforts in clinical studies of new agents which are representative of steroidal selective estrogen receptor down-regulator, cyclin-dependent kinase (CDK) 4/6 inhibitors, inhibitors of the PI3K/AKT/mTOR Pathway and histone deacetylase (HDAC) Inhibitors. Our studies at LBCB focused the endocrine resistance in young age and showed that age under 35 years is poor prognostic factor on not only single-center data but also Korean Breast Cancer Registry Data and that women with hormone receptor-positive breast cancer who were younger than 35 years of age had less response to anti-hormonal therapy. Also, a study for gene expression in hormone receptor-positive breast cancer at a very young age (<35) revealed that expression of cell cycle-related genes increased higher than that of premenopausal women in their forties. There have been a lot of studies and clinical trials to investigate the mechanisms of resistance to endocrine treatment and to overcome them with new drugs. However, many still do not know the precise mechanism of recurrence of breast cancer after endocrine treatment. In particular, the identification of the mechanism of endocrine resistance in young women, and the combination of drugs and clinical trials to overcome this require much effort.
Keywords: Age; Breast neoplasm; Hormones; Resistance; Young.