Depending on the amounts present, reactive oxygen species can exert either beneficial or deleterious effect to cells. In the present study, we observed a decrease in cell viability concomitant with an increase of malondialdehyde concentration in hydrogen peroxide (H(2)O(2))-treated MCF-7 breast cancer cells. There was also a concurrent G1/S phase cell cycle arrest with increased apoptosis in H(2)O(2)-treated cells. Analysis of 84 oxidative stress related genes showed that five genes were significantly and differentially regulated, namely, Cytoglobin (CYGB), Forkhead box M1 (FOXM1), NADPH oxidase (NOX5), Nudix (nucleoside diphosphate linked moiety X)-type motif 1 (NUDT1) and Selenoprotein P1 (SEPP1) genes with H(2)O(2) treatment. It would seem that oxidative stress induces cell cycle arrest in the breast cancer by modulation of these genes. Manipulation of these genes, in particular FOXM1, a proliferation-specific gene associated with human malignancies, could stifle cancer progression and enhance the therapeutic efficacy of drugs which exert their effects by oxidative stress.