ERBB2 and breast cancer: According to the recommendations of the 2013 American Society of Clinical Oncology and College of American Pathologists (ASCO/CAP) guidelines for HER2 breast cancer testing, an additional test should be pursued on a different block from the same tumor as one of the options for patients with immunohistochemistry (IHC) 2+ and a HER2/CEP17 ratio of < 2.0 with an average HER2 signals per tumor cell of ≥ 4.0 and < 6.0 by reflex test using dual-probe fluorescence in situ hybridization (FISH) (double-equivocal HER2).