Tumor biology in estrogen receptor-positive,human epidermal growth factor receptor type 2-negative breast cancer:Mind the menopausal status

Breast cancer is not one disease,but can be categorized into four major molecular subtypes according to hormone receptor [estrogen receptor(ER) and progesterone receptor(Pg R)] and human epidermal growth factor receptor type 2(HER2) expression status. Ki67 labeling index and/or multigene assays are used to classify ERpositive,HER2-negative breast cancer into luminal A and luminal B(HER2-negative) subtypes. To date,most studies analyzing predictive or prognostic factors in ER-positive breast cancer have been performed in postmenopausal women,mainly using patients and samples in adjuvant aromatase inhibitor trials. In contrast,even the clinical roles of Pg R and Ki67 have been little analyzed so far in premenopausal women. Pg R is one of the estrogen-responsive genes,and it has been reported that plasma estradiol levels are related to expression levels of estrogen-responsive genes including PGR in ER-positive breast cancer. In this article,biological differences,especially differences in expression of Pg R and Ki67 in ER-positive breast cancer between pre- and postmenopausal women are discussed. Clinical roles of Pg R and Ki67 in ER-positive breast cancer differ between pre- and postmenopausal women. We suggest that the mechanisms of development and estrogen-dependent growth of ER-positive breast cancer might differ according to menopausal status.