DDIT3 and breast cancer: Notably, DDIT3, a key regulator of ER stress and cellular apoptosis, was induced by both O-desmethyltramadol and tramadol in MCF-7 and MDA-MB-231 cells; however, its induction was less pronounced with O-desmethyltramadol, suggesting a potential difference in the regulation of stress-related pathways in breast cancer cells.