Cytochrome P450 2J2 (CYP2J2) epoxygenase converts arachidonic acid to four regioisomeric epoxyeicosatrienoic acids (EETs) that exert multiple biological effects in the cardiovascular system and in various human solid cancers. However, it is unknown whether this enzyme is expressed or plays any role in malignant hematological diseases. In this study, we found strong and highly selective CYP2J2 expression in five human-derived malignant hematological cell lines and in leukemia cells from peripheral blood and bone marrow in 36 of 42 patients (86%) with malignant hematologic diseases. Furthermore, increased levels of EETs were detected in urine and blood samples from these patients. Addition of exogenous EET or CYP2J2 overexpression in cultured human-derived malignant hematologic cell lines markedly accelerated proliferation and attenuated apoptosis. Addition of the selective CYP2J2 inhibitor compound 26 (C26; 1-[4-(vinyl) phenyl]-4-[4-(diphenyl-hydroxymethyl)-piperidinyl]-butanone hydrochloride) inhibited cell proliferation and increased apoptosis, an effect that was significantly reversed by EET. CYP2J2 overexpression and exogenous EET activated AMP-activated protein kinase, c-Jun NH(2)-terminal kinase, and phosphatidylinositol 3-kinase/Akt signaling pathways, and increased epidermal growth factor receptor phosphorylation levels. CYP2J2 overexpression also enhanced malignant xenograft growth, which was efficiently inhibited by oral administration of C26 in Tie2-CYP2J2 transgenic mice and in severe combined immunodeficiency (SCID) xenograft mice. Together, these results suggest that CYP2J2 plays a key role in the pathogenesis of human hematologic malignant diseases. Selective inhibition of CYP2J2 may be a promising therapeutic strategy for these conditions.