Effectiveness and Safety of Palbociclib: Brand vs. Generic in Iraqi Stage IV Breast Cancer Patients

Inclusion Criteria: 1. Females ≥ 18 years. 2. Histological or cytological confirmation of HR+/HER2- advanced or metastatic breast cancer according to international criteria for pathology. 3\. Patients evaluated prior to treatment with letrozole or fulvestrant having had at least 1 cycle of palbociclib (retrospectively, Ibrance® or prospectively, Palbociclib-IPI) for HR+/HER2- advanced or metastatic breast cancer. 4\. Availability of a complete history and physical examination, laboratory tests, and imaging studies of the patients, including baseline and follow-up tests and examinations. 5\. For the prospective group, the patients had to be willing to give informed consent for evaluation of quality of life and for evaluation of medical data. Exclusion Criteria: 1. Male breast cancer patients, due to a different biology and small population proportion in Iraq. 2\. Patients with HER2-positive or triple-negative breast cancer, due to different algorithms for treatment and prognosis. 3\. Patients previously receiving CDK4/6 inhibition apart from palbociclib (ribociclib or abemaciclib) so as to not have biased results. 4\. Patients without complete medical history or follow-up sufficient to evaluate reliable outcomes. 5\. Patients with other cancers or severe comorbidities which had a direct impact on survival results independent of breast cancer per criteria done in other real-world observational cohorts \-