According to the guidelines set forth by the American Society of Clinical Oncology-College of American Pathologists (ASCO-CAP), HER2 positivity is defined as tumors that exhibit 3+ positive staining by immunohistochemistry (IHC) in at least 10% of tumor cells, or detection of HER2 gene amplification through fluorescence in situ hybridization (FISH)4. This evidence concerns the gene ERBB2 and neoplasm.