CASP3 and breast cancer: Human breast cancer cells MDA-MB-231, MCF7, and ZR75-1 cultured in suspension, mimicking the bloodstream environment, lowered protein levels of Fas, TNF-α receptor, and death receptor 5 (DR5), death receptors that initiate extrinsic apoptosis [93], and this impaired the activation of caspase 3 compared to the adherent group [93].