Inclusion Criteria:  Postmenopausal women (defined as those with permanent cessation of menstruation for more than 12 months, regardless of whether their menopausal condition occurred naturally or was artificially induced), ambulatory or hospitalized Diagnosis of advanced breast cancer HR +, HER2- Positivity for hormone receptors (either estrogen, progesterone, or both). Negative for human epidermal growth factor receptor 2 (HER2). Acceptance of informed consent, if it is required by local regulatory standards.  Exclusion Criteria  History of previous treatment with fulvestrant. Concomitant treatment with antitumor drugs other than cyclin inhibitors (abemaciclib, palbociclib, ribociclib). Pregnancy. Lactation. Hypersensitivity to any of the excipients included in the complete formulation of fulvestrant from Dr. Reddy's Laboratories Limited. Renal insufficiency grade 4 or 5 (creatinine clearance <30 ml / min / 1.73 m2 according to the classification of the National Kidney Foundation). Hepatic failure (Child-Pugh C stage). Performance status ECOG ≥ 3.