Postpromotional effects of dietary marine or safflower oils on large bowel or pulmonary implants of CT-26 in mice.

Marine oils containing n-3 fatty acids exhibit variable antineoplastic effects. Diets containing low (11.6% of kcal) or high (46.5% of kcal) levels of marine oils as the exclusive fat source were compared to diets containing identical amounts of safflower oil (n-6) in weanling, male BALB/c ByJ mice. All diets provided approximately 90 kcal/100 g body weight/day, and contained identical quantities of vitamins, minerals, protein, and fiber. The growth of transplantable colon carcinoma, CT-26, (10(6) cells/animal) implanted, subserosally, into the descending colon via laparotomy, was observed weekly over 28 days by necropsy in all dietary groups. At each time period animals fed safflower oil had larger tumors than those fed marine oil. Tumor volumes at 21 days postimplantation were as follows: low fat marine, 55 mm3 (5-196 mm3) [median (range)]; high fat marine, 70 (26-194); low fat safflower, 216 (32-800); high fat safflower, 247 (70-1352). Marine oil tumors were smaller than safflower oil tumors (P less than 0.005 by analysis of variance; P less than 0.01 by Scheffe test). Metastatic potential was assessed by pulmonary colonization. CT-26 was injected i.v. in tail veins (10(5) cells/animal). Mice were sacrificed and colonies were counted after 21 days. Mice fed low fat marine, high fat marine, and low fat safflower oil diets, 10-14 colonies; high fat safflower, 55 colonies (P less than 0.001 by analysis of variance). Hence, dietary marine oil significantly suppressed growth of this colon carcinoma at all intake levels studied and inhibited pulmonary colonization at higher intakes relative to safflower oil.