In cases with 2+ expression by IHC (i.e., being equivocal, weak to moderate complete or basolateral or lateral membranous reactivity in ≥ 10% of cancer cells), then in situ hybridization cutoffs using either the HER2/CEP17 (centromeric region of chromosome 17) ratio or copy number–based assessment can be used to delineate final HER2 status. The gene discussed is ERBB2; the disease is cancer.