I take the NOW brand "ultra-omega 3" (500EPA/250DHA), and take what I have read as beneficial against esophageal cancer. I chose it in terms of EPA and DHA content.
I take 2 in the morning and 1 in the evening. I don't trust just one study or necessarily a number of studies for that matter, but given that fish oil does many positive things I decided that I might as well take it (as one of the few supplements that I believe in).
Here is the study I saw.
Fish oils may help prevent esophageal cancer
NORWICH, UNITED KINGDOM. Cancer of the esophagus has a poor prognosis and is increasing in frequency. Esophageal cancer is usually preceded by a condition called Barrett's esophagus (BE) in which the normal squamous (scale-like) epithelium in the lower esophagus is replaced with columnar epithelium. about 5% of patients with BE progress to esophageal cancer. BE, in turn, is linked to gastroesophageal reflux disease (GERD) with from 10-20% of GERD patients progressing to BE.
Research has shown that colon cancer is associated with an increased expression of the COX-2 enzyme in the colon and that fish oil can reduce both the COX-2 level and the risk of colon cancer. There is also evidence that the COX-2 enzyme is upregulated in Barrett's esophagus and esophageal cancer. British researchers therefore reasoned that fish oil supplementation might also be beneficial in BE and thus, indirectly, lower the risk of esophageal cancer.
Their clinical trial involved 46 patients with previously diagnosed BE. Twenty-seven of them were assigned to receive 3 EPA (eicosapentaenoic acid) capsules daily providing a total EPA intake of 1.5 grams a day with the remaining 19 patients serving as controls. Before the start of supplementation and at the end of the 6-month trial period, all participants underwent endoscopy during which appropriate biopsy samples were obtained. Analysis of the samples showed a significantly increased concentration of EPA and a significantly decreased level of COX-2 proteins in BE tissue in the supplement group, but not in the control group.
The researchers conclude that regular supplementation with relatively small doses of EPA results in significant incorporation of metabolically active long-chain amoega-3 fatty acids into BE tissue and a concomitant, beneficial decrease in COX-2.
Mehta, SP, et al. Effect of n-3 polyunsaturated fatty acids on Barrett's epithelium in the human lower esophagus. American Journal of Clinical Nutrition, Vol. 87, 2008, pp. 949-56