4-oxo Docosahexaenoic acid (4-oxo DHA) is a putative metabolite of DHA with antiproliferative and PPARγ agonist activity. It inhibits the growth of several triple negative breast cancer cell lines (MCF-10F, trMCF, bsMCF, MDA-MB-231, and BT549) at 50-100 µM, however it increased proliferation of MCF-7 cells. 4-oxo DHA binds covalently to PPARγ and activates gene transcription in luciferase reporter assays and in dendritic cells with EC50 values of approximately 8-16 µM.