NOX4 and breast carcinoma: Furthermore, stromal NOX4 seems to be a molecular target of TGF-β1 present in media conditioned by breast carcinoma cell lines, as was confirmed by the use of the TβRI inhibitor SB431542 that totally abolished the expression of NOX4 stimulated by media conditioned by MCF-7 and by MDA MB-231 cells, a more invasive cell line that secretes four times more TGF-β1 than MCF-7 (Guerrero et al, 2010).