Introduction: Cancer has been associated with increased oxidative stress and deregulation of bioactive oxylipins derived from long-chain polyunsaturated fatty acids (LC-PUFA) like arachidonic acid (AA). There is a debate whether -3 LC-PUFA could promote or prevent prostate tumor growth through immune modulation and reduction of oxidative stress. Our aim was to study the association between enzymatically or non-enzymatically produced oxidized-LC-PUFA metabolites and tumor growth in an immune-competent eugonadal and castrated C57BL/6 male mice injected with TRAMP-C2 prostate tumor cells, fed with -3 or -6 LC-PUFA-rich diets. Materials and methods: Tumor fatty acids were profiled by gas chromatography and 26 metabolites derived from either AA, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were assessed by liquid chromatography-mass spectrometry. Results: The enriched -3 diet did not reduce oxidative stress overall in tumors but favored the formation of -3 rather than -6 derived isoprostanoids. We discovered that EPA and its oxidized-derivatives like F3-isoprostanes and prostaglandin (PG)F3, were inversely correlated with tumor volume (spearman correlations and T-test, p<0.05). In contrast, F2-isoprostanes, adrenic acid, docosapentaenoic acid (DPA- 6) and PGE2 were positively correlated with tumor volume. Interestingly, F4-neuroprostanes, PGD2, PGF2, and thromboxane were specifically increased in TRAMP-C2 tumors of castrated mice compared to those of eugonadal mice. Discussion: Decreasing tumor growth under -3 diet could be attributed in part to increased levels of EPA and its oxidized-derivatives, a reduced level of pro-angiogenic PGE2 and increased levels of F4- neuroprostanes and resolvins content in tumors, suspected of having anti-proliferative and anti- inflammatory effects