To study the functional relevance of As2O3-mediated alteration of Notch-1 expression in breast cancer cells, we used Notch-1 siRNA to deplete the endogenous expression of Notch-1 and subsequently examined the effect of Notch-1 siRNA on cell growth and apoptosis followed by 8 μM As2O3 treatment in SKBR-3 cells. The gene discussed is NOTCH1; the disease is breast carcinoma.