The breast cancer cell line MDA-MB-231 (p53 mutant, HER-2 negative, estrogen receptor negative, progesterone receptor negative) is representative for high-malignancy and therapy-refractory breast cancer, and we show that oxidant-induced apoptosis can be increased more than 33% by either inhibiting nNOS or Grp94. This evidence concerns the gene ESR1 and breast carcinoma.