We report the case of a 38-year-old woman with estrogen/progesterone receptor negative (ER/PR-), human epidermal growth factor receptor 2 positive (HER2+) invasive ductal carcinoma of the left breast who underwent bilateral mastectomies with axillary lymph node dissection and chemotherapy treatment. The gene discussed is ERBB2; the disease is invasive ductal breast carcinoma.