Similarly, if the rate of HER2(+) breast cancer is accepted as 20%, 5.4% of the remaining 80% patient group will be considered HER2(−) according to tru-cut biopsy results, even though they are HER2(+), and approximately 4–5% of these patients will be devoid of anti-HER2 treatments. The gene discussed is ERBB2; the disease is breast carcinoma.