A phase IV, single arm study will be performed in postmenopausal women with locally advanced or metastatic breast cancer. All patients included will receive fulvestrant from Dr. Reddy's Laboratories, in accordance with local practice and the regulatory authorization of the drug in Colombia. This study will be carried out for 1 year and approximately 40 patients will be included in 2 research centers selected for its conduct.

Patients who meet the inclusion criteria and who do not have to be discarded from entering the study due to meeting any of the exclusion criteria, will be evaluated to determine the effectiveness and tolerability of the administration of Dr. Reddy's fulvestrant at a dose of 500 mg / month plus an additional indicated dose 14 days after the initial dose, for 12 months of follow-up or until disease progression or the appearance of unacceptable toxicity. The assessment of tolerability will be carried out based on the collection of data related to adverse events from the first dose administered.

Inclusion Criteria:

1. 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
2. Diagnosis of advanced breast cancer HR +, HER2-
3. Positivity for hormone receptors (either estrogen, progesterone, or both).
4. Negative for human epidermal growth factor receptor 2 (HER2).
5. Acceptance of informed consent, if it is required by local regulatory standards.

Exclusion Criteria

1. History of previous treatment with fulvestrant.
2. Concomitant treatment with antitumor drugs other than cyclin inhibitors (abemaciclib, palbociclib, ribociclib).
3. Pregnancy.
4. Lactation.
5. Hypersensitivity to any of the excipients included in the complete formulation of fulvestrant from Dr. Reddy's Laboratories Limited.
6. Renal insufficiency grade 4 or 5 (creatinine clearance <30 ml / min / 1.73 m2 according to the classification of the National Kidney Foundation).
7. Hepatic failure (Child-Pugh C stage).
8. Performance status ECOG ≥ 3.

Postmenopausal Women with Advanced Breast Cancer HR+, HER2-