Abstract Metastatic breast cancer (BC) is a highly invasive form of cancer that contributes greatly to patient mortality. Due to the complex mechanisms underlying cancer growth and metastasis, novel therapeutic targets must be found to increase patient survival. One such target is the cytochrome P450 4 (CYP4) metabolic pathway leading to the production of 20-hydroxyeicosatetraenoic acid (20-HETE). 20-HETE is a lipid signaling molecule that promotes both tumor cell proliferation and neovascularization in tumors by inducing the proliferation and migration of endothelial cells, therefore promoting BC tumor survival. N-hydroxy-N’-(4-butyl-2 methyl phenyl) formamidine (HET0016) is a selective inhibitor of 20-HETE synthesis, thus impairing tumor growth and neovascularization. This study aims to investigate changes in BC (MDAMB231 and MCF7) cell lines overexpressing CYP4A11, a human CYP4 enzyme, with and without HET0016 treatment. To accomplish this, cells that overexpressed CYP4A11 were produced using lentivirus infection and confirmed via western blot. Tumor cell aggressiveness was assessed in vitro using migration and proliferation assays. Tumor growth with and without CYP4A11 overexpression was also measured in vivo using athymic nude mice. The results demonstrated that cells overexpressing CYP4A11 showed protein levels 4 times higher than the non-modified cells. MDAMB231 is a triple-negative BC (TNBC) that, when overexpressing CYP4A11, demonstrated increased proliferation capacity and significant increased tumor growth compared to non-modified cells. TNBC cells overexpressing CYP4A11 also showed increased motility. However, modified MCF7 cells did not show significant alterations when compared to non-modified MCF7 cells. Additionally, all cells treated with HET0016 showed decreased migration in the first 24 hours. In conclusion, these results demonstrate that the overexpression of CYP4A11 in TNBC cells increased tumor aggressiveness, proving this pathway to be an important target for therapeutic inhibition. Citation Format: Sehar Ali, Thaiz Borin, Ali Arbab. Evaluation of cytochrome P450 4A11 overexpression in breast cancer cells in vitro and in vivo [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-16-08.