Moreover, RQ-PCR analysis revealed that the enhanced cytotoxic effect of As2O3 in the presence of melatonin is mediated, at least partly, through suppressing the expression of NF-κB anti-apoptotic target genes such as MCL-1, BCL-2, survivin, XIAP, and c-IAP1 in breast cancer cells. The gene discussed is XIAP; the disease is breast cancer.