Arm A: Pre- or perimenopausal women are treated with tamoxifen, alternatively with an LHRH analogue in combination with an aromatase inhibitor (only women). Postmenopausal women receive an aromatase inhibitor. The preoperative treatment is continued for further 12 weeks, provided that re-evaluation after 6 and 10 weeks of the preoperative treatment does not indicate progression. Upon progression (PD), individualized management, preferentially surgery, is the primary option.