N-desmethyltamoxifen, resulting from the CYP3A4/5-mediated catalysis of tamoxifen, is the major primary quantitative metabolite of tamoxifen. N-desmethyltamoxifen (20-500 ng/ml; 48 hours) has a profound inhibitory effect upon all seven glioma lines (T98G, U87, U138, U373, ALW, AUK, CAS cells). N-desmethyltamoxifen (1.5-10 μM; 114 hours) suppresses the growth of MCF 7 human mammary carcinoma cells. [1][2][3].