Inclusion Criteria:  Male or female patients who have at least 18 years of age at enrollment.  Patients with locally recurrent or advanced inoperable breast cancer diagnosed between January 2015 and January 2020.  AND/OR  Patients with early breast cancer diagnosed between 2005 and 2020.  Pathologically documented breast cancer that:  Has a history of HER2-positive expression (defined as immunohistochemistry [IHC] 3+ or concurrent IHC 2+ with in situ hybridization [ISH]- positive) or HER2-low expression (defined as IHC 2+ with ISH-negative or IHC 1+ with ISH-negative or untested) or HER2-negative expression (defined as IHC 0) with a validated assay according to American Society Of Clinical Oncology-College of American Pathologists (ASCO/CAP) recommendations at the time of diagnose, during early and/or advanced setting.  Note: In patients with locally recurrent or advanced inoperable breast cancer, HER2 expression should have been performed on the most recent tumor biopsy since last progression from metastatic tissue.  Is documented as hormone receptor (HR)-positive (either estrogen receptor [ER]- and/or progesterone receptor [PgR]-positive [ER or PgR ≥1%]) or HR- negative (ER- and PgR-negative [ER and PgR <1%] per ASCO/CAP guidelines during early and/or advanced setting.  Has documented progression during or after prior treatment in the adjuvant or neo-adjuvant setting.  Electronic Health Records (EHRs), with guaranteed data to meet requisites, about clinicopathological characteristics, type of surgery, treatment management, disease outcomes, and genomic profile. Centers that agree to participate must commit to include all subjects who meet the inclusion criteria, in order to reduce possible selection bias.  Exclusion criteria:  Medical charts at Hospital that cannot guarantee reliable and congruent EHRs. If sufficient data cannot be obtained from EHRs.