Use of aspirin for cancer prevention and treatment have been reported extensively in recent years. But inconsistent results and unclear molecular mechanism of aspirin on cancer argu that it should be more cautious of using aspirin for long-term prevention for cancer [1-4]. In this study, we took aspirin as bait and put it in the comparative toxicogenomics database to search for all potential protein targets of aspirin against disease. These protein targets were subjected for GO enrichment analysis using the metascape online website. Meanwhile, p-value was corrected by false discovery rate (FDR). The threshold of p-value less than 0.5 was set as significantly related biological process. Finally, obtained differentially expressed genes were subjected to KEGG pathway enrichment analysis to find significant differences biological regulatory pathways. Human breast cancer cells were then cultured in vitro with aspirin to observe the changes in cancer cell phenotype and to select the signal pathway to be studied. Based on the results of KEGG pathway enrichment analysis and in vitro cell culture phenotypic changes study, we chose two downstream key molecules of the MAPK signaling pathway, VEGF and MMP, as candidates to study. The effects of aspirin on breast cancer cells were verified by cell experiments and molecular experiments. Meanwhile, we added platelets as experimental variables in the experimental group to investigate whether platelets can interfere with this effect of aspirin. In vivo breast cancer mouse model was also used. A total of 714 aspirin protein targets were obtained through searching the comparative toxicogenomics database. The results of GO enrichment analysis showed that the top 10 biological processes with the highest correlation with aspirin were cytokine-mediated signaling pathway, positive regulation of cell death, response to lipopolysaccharide, inflammatory response, response to inorganic substance, fluid shear stress and atherosclerosis, apoptosis, response to wounding, response to toxic substance, and pathways in cancer. In vitro results showed that aspirin has an inhibitory effect on the proliferation and migration on tumor cells. Aspirin can block the in vitro epithelial-mesenchyme transformation of breast cancer cells and down-regulate the expression of VEGF and MMP-9. Platelets however played the opposite effect. After co-cultivation of aspirin, platelets and cancer cells, aspirin and platelets could interfere with each other. In vivo breast cancer mouse model experiments showed the similar results. In conclusion, our results indicate that aspirin can affect multiple biological processes in the organism. Aspirin can inhibit the development of breast cancer at the cellular level or organism to some extent. The mechanism to inhibit the development of cancer may be due to inhibiting the epithelial-mesenchymal transition of tumor cells and down-regulating the expression of VEGF and MMP-9.