Induces DNA fragmentation, cleavage of poly(ADP-ribose) polymerase and caspase-3, and promotes cell death of both trastuzumab-naive and trastuzumab-refractory HER2-overexpressing breast cancer cells. NDGA and trastuzumab suppressed proliferation and survival of trastuzumab-refractory cells to a greater degree than either agent alone. This evidence concerns the gene ERBB2 and breast carcinoma.