9Z,11E,13E-octadecatrienoic acid (α-ESA) is a conjugated polyunsaturated fatty acid commonly found in plant seed oil. This fatty acid accounts for about 60% of the total fatty acid composition of bitter gourd seed oil and about 70% in tung oil. α-ESA is metabolized and converted to conjugated linoleic acid (9Z,11E-CLA) in rats. It has shown potential as a tumor growth suppressor. In colon cancer Caco-2 cells, α-ESA induced apoptosis through up-regulation of GADD45, p53, and PPARγ. In DLD-1 cells supplemented with α-ESA, apoptosis was induced via lipid peroxidation with an EC50 of 20 µM. It also inhibits DNA polymerases and topoisomerases with IC50s ranging from ~5-20 µM for different isoforms of the enzymes. α-ESA methyl ester is a neutral, more lipid soluble form of the free acid.