This noninterventional, multicenter,retrospective study has been proposed to estimate the prevalence, clinicopathological characteristics,treatment patterns and clinical outcomes of human epidermal growth factor receptor 2 -(HER2)low locally-advanced or metastatic breast cancer(mBC) by accurate rescoring of archived IHC-stained formalin-fixed paraffin-embedded (FFPE) slides for HER2 in patients previously identified as HER2-negative from emerging markets of international regions (non-US and non-European region) with largely unknown prevalence estimates of HER2 low mBCs. Patients with a confirmed diagnosis of HER2-negative, locally-advanced or mBC regardless of Hormone receptor (HR)status between 01 January 2019 and 31 December 2022 who progressed on any systematic anticancer therapy (eg, ET, chemotherapy, CDK4/6 inhibitor, targeted therapies other than anti-HER2, or immunotherapy) in advanced disease with availability of atleast 12 months of follow-up data (from the index date) in the medical records at the participating site, unless patient died within the first 12 months of diagnosis of locally-advanced or mBC will be enrolled in the study. The HR positive patients will be considered eligible for the study if they have received ET as adjuvant therapy in the early BC setting and progressed within 24 months. This scenario will be considered as progression on systematic treatment in the advanced or metastatic setting.
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Proportion of patients with IHC 1+ or IHC 2+/ISH- HER2 expression.
Timeframe: 6 months from the Last subject In
Proportion of patients with HER2 ultra-low (IHC 0 (pattern 0+) with membrane staining ie, incomplete and faint/barely perceptible in ≤10% tumor cells) HER2 expression and IHC null (IHC 0 ie, absent membrane staining),
Timeframe: 6 months from the Last subject In