 - Arm I chemotherapy first: Beginning within 4 weeks after randomization, patients receive chemotherapy comprising either an anthracycline- or a taxane-based regimen, or a combination of both drugs, according to local institutional guidelines. Treatment continues for 6 months or longer, in the absence of disease progression or unacceptable toxicity. After discontinuation of chemotherapy, patients receive endocrine therapy comprising oral letrozole once daily in the absence of disease progression or unacceptable toxicity. Patients with immediately life-threatening disease e.g., lymphangitis carcinomatosa or liver involvement exceeding 13 of the liver are recommended for second-line chemotherapy. 