抄録
For the treatment of patients with metastatic breast cancer by humanized anti-human epidermal growth factor receptor type 2 (HER2) antibody (trastuzumab), it is important to evaluate HER2 status adequately. This article overviews developments of basic and clinical research for HER2 gene, and introduces general agreement with the evaluation system of HER2 overexpression with several commentaries from the aspect of histochemistry.