ObjectiveTo investigate the effects of phenethyl isothiocyanate (PEITC) on apoptosis and proliferation of breast cancer SK-BR-3 cells. MethodsSK-BR-3 cells were treated with different concentrations (0, 10, 30, 50 μmol/L) of PEITC respectively. The proliferation capacity of SK-BR-3 cells was detected by MTT and BrdU staining methods. The cell apoptosis was detected by TUNEL and flow cytometry methods. The protein and mRNA expressions levels of indexes related apoptosis such as Bcl-2, Bax, and MCL-1 and indexes related endoplasmic reticulum stress (ERS) such as PERK, eIF2α, CHOP, IRE1α, ATF6α were detected by Western blot and quantitative real-time PCR (qRT-PCR), respectively. ResultsCompared with the control group (0 μmol/L PEITC treatment group), the results of MTT and BrdU staining methods showed that the proliferations of SK-BR-3 cells in the 10, 30 and 50 μmol/L PEITC treatment group were decreased in turn with the increase of concentration. The results of TUNEL and flow cytometry methods showed that the apoptosis rates of SK-BR-3 cells in the 10, 30 and 50 μmol/L PEITC treatment group were increased in turn with the increase of concentration. The results of Western blot and qRT-PCR methods showed that the protein and mRNA expression levels of anti-apoptotic indexes (Bcl-2, MCL-1) were decreased with the increase of concentration, while the expression levels of protein and mRNA of the pro-apoptotic index (Bax) and ERS-related indexes (PERK, eIF2α, CHOP, IRE1α, ATF6α) increased with the increase of concentration. ConclusionFrom the preliminary results of this study, PEITC can promote the apoptosis of breast cancer SK-BR-3 cells and inhibit cell proliferation, which might be achieved by regulating the expression levels of indexes related apoptosis and ERS.