While HER2-positive breast cancer only accounts for about 20% of new diagnoses, a greater proportion of patients (approximately 40–50%) have HER2 expression categorized as IHC 1+ or 2+ but FISH negative; moreover, this BC subgroup is classified with 0+ at IHC as HER2-negative for treatment decisions, excluding anti-HER2 therapies [14]. The gene discussed is ERBB2; the disease is breast carcinoma.