- Postmenopausal women (postmenopausal: age >= 60 years, or amenorrhea >= 12 months, or bilateral oophorectomy, or - in women with hysterectomy only - follicle stimulating hormone [FSH] in the menopausal levels as per local institutional guidelines if < 60 years old) with histologically-confirmed estrogen receptor (ER) positive (>= 10%) primary breast cancer stage T0-2, N0-1, Mx; women with larger tumors who refuse chemotherapy (chemo) and/or endocrine neoadjuvant therapy can be eligible