We previously found cytotoxic effects of tomato leaf extract (TLE) on the MCF-7 breast cancer cell line. Theaim of this study was to ascertain the molecular mechanisms associated with the usage of TLE as an anticanceragent by microarray analysis using mRNA from MCF-7 breast cancer cells after treatment with TLE for 1 hrand 48 hrs. Approximately 991 genes out of the 30,000 genes in the human genome were significantly (p<0.05)changed after the treatment. Within this gene set, 88 were significantly changed between the TLE treated cellsand the untreated MCF-7 cells (control cells) with a cut-off fold change >2.00. In order to focus on genes thatwere involved in cancer cell growth, only twenty-nine genes were selected, either down-regulated or up-regulatedafter treatment with TLE. Microarray assay results were confirmed by analyzing 10 of the most up and downregulated genes related to cancer cells progression using real-time PCR. Treatment with TLE induced significantup-regulation in the expression of the CRYAB, PIM1, BTG1, CYR61, HIF1-α and CEBP-β genes after 1 hr and48 hrs, whereas the TXNIP and THBS1 genes were up-regulated after 1 hr of treatment but down-regulatedafter 48 hrs. In addition both the HMG1L1 and HIST2H3D genes were down-regulated after 1 hr and 48 hrs oftreatment. These results demonstrate the potent activity of TLE as an anticancer agent.