Because caspase 8 is involved in the extrinsic pathway of apoptosis and affects the intrinsic pathway of this process [13,14,15], we examined the impact of novel selenoesters (EDAG-1 and EDAG-8) as well as cisplatin on caspase 8 activity in MCF-7 and MDA-MB-231 breast cancer cells following a 24 h exposure (concentrations of 0.5 and 1 μM) to those compounds. The gene discussed is HEMGN; the disease is breast carcinoma.