Highlights of the cancer chemoprevention studies in China.

New retinoids have been synthesized and screened in the search for chemopreventive agents of cancer. N-4-(Carboxyphenyl) retinamide showed a significant inhibitiory effect on carcinogenesis of cancers in the buccal pouch of hamsters and in the forestomach of mice. Clinical studies have demonstrated that N-4-(carboxyphenyl) retinamide is effective against oral leukoplakia, vulvar leukoplakia, and dysplasia of the uterine cervix and stomach. Field studies among a population at high risk for esophageal cancer in Linxian County, Henan Province, revealed that N-4-(ethoxycarbophenyl) retinamide decreased the incidence of this cancer. Qidong County is a high-risk area for hepatoma in China. This has been correlated to the low levels of selenium in the blood of the residents as well as in grain grown in the area. S. Y. Yu, W. G. Li, Y. J. Zhu, et al. (Biol. Trace Element Res. 1985; 7:22-26) reported that the administration of selenium inhibited the incidence of hepatoma induced by aflatoxin B in rats and in ducks. Experimental studies demonstrated that green tea extract inhibited 12-O-tetradecanoylphorbol-3-acetate-induced epidermal ornithine decarboxylase activity and counteracted 12-O-tetradecanoylphorbol-3-acetate-induced ear edema in mice. It is interesting that green tea extract inhibited the transformation of Balb/c 3T3 cells induced by methylcholanthrene and 12-O-tetradenanoylphorbol-3-acetate. Garlic has been used for thousands of years in Chinese cooking and folk medicine. Epidemiological studies show that the dietary intake of garlic is inversely related to gastric cancer incidence in Shandong Province.