Although TB also induced cytotoxicity in triple-negative MDA-MB-231 (IC50 28.07 μM) and HER2+ SK-BR-3 (IC50 12.8 μM) cells, its significantly higher activity in ER+ MCF-7 (IC50 7.2 μM) cells led us to focus our mechanistic investigations on this line. The gene discussed is ERBB2; the disease is tuberculosis.