ESR1 and breast cancer: In the present study, we used ultra performance liquid chromatography–mass spectrometry (UPLC‐Orbitrap‐MS) and gas chromatography–mass spectrometry (GC‐MS) to evaluate whether SFN could alter the effects of estrogen on major metabolic pathways that are constitutively active, with particular emphasis on tumorigenicity by epigenetic pathway in estrogen receptor positive (ER+) breast cancer.