**4. Conclusions**

Quantitative proteomic analysis of breast cancer cell lines allowed us to identify several proteins whose abundance (FC) increased more than 1.5×, and proteins that abundance decreased less than 0.67×, after 24 h treatment with *B. jararaca* at either low sub-toxic dose of 0.63 μg/mL or high sub-toxic dose of 2.5 μg/mL. Most of these proteins identified suggest that the treatment with the venom may activate mitochondrial apoptotic pathways leading cells to death. In addition, several of the identified proteins play important roles related to cell proliferation, invasion, metastasis, apoptosis, and stress response. Therefore, these data show that *B. jararaca* venom or some of its toxin or components can inhibit tumor cell proliferation and survival and can potentially be used to identify novel targets for cancer therapy.
