Background: Invasive micropapillary carcinoma (IMPC) is a specific subtype of breast cancer with cell polarity reversal. This distinct morphology of IMPC can affect the immunohistochemical (IHC) staining of human epidermal growth factor receptor-2 (HER2), and tumor cells usually show an incomplete membranous staining pattern. Material and Methods: Using the 2023 American Society of Clinical Oncology and the American College of Pathologists (ASCO/CAP) Guideline on HER2 testing, IHC results for HER2 were retrospectively reassessed in 281 consecutive patients with IMPC who were admitted in the Fourth Hospital of Hebei Medical University from January 2015 to June 2023. Since most cases were mixed breast cancers with invasive micropapillary components ranging from 10% to 100%, only the HER2 status of the invasive micropapillary region was reassessed. With reference to the hematoxylin and eosin-stained sections of each case, other types of invasive breast cancer and ductal carcinoma in situ components were removed from its formalin-fixed paraffin-embedded (FFPE) tissue blocks. ERBB2 mRNA level of all processed FFPE samples were detected by MammaTyper® (Cera Biotech GmbH, Berlin), a quantitative real-time polymerase chain reaction (RT-qPCR) kit for breast cancer subtyping, and fluorescence in situ hybridization (FISH) was performed for HER2 IHC 2+ cases.