Update from Asia. Asian studies on cancer chemoprevention.

In Asia, nontoxic dietary products are considered desirable primary prevention vehicles for conquering cancer. As early as 1978, investigators in Korea carried out extensive long-term anticarcinogenicity experiments using the mouse lung tumor model and observed an anticarcinogenic effect of Panax ginseng C.A. Meyer extract in 1980. The results showed that natural products can provide hope for human cancer prevention. A newly established nine-week medium-term model using mouse lung tumors (Yun's model) could confirm the anticarcinogenicity of ginseng that varies according to its type and age. Subsequently, the ginseng was shown by epidemiological studies to be a nonorgan-specific cancer preventive agent associated with a dose-response relationship. The anticarcinogenic effects of vegetarian foods common at every dining table in Korea and some synthetics were also studied using Yun's nine-week model. In brief, ascorbic acid, soybean lecithin, capsaicin, biochanin A, Ganoderma lucidum, caffeine, and a novel synthetic 2-(allylthio)pyrazine decrease the incidence of mouse lung tumors, whereas fresh ginseng (4 years old), carrot, spinach, Sesamum indicum, beta-carotene, and 13-cis retinoic acid do not. This result regarding beta-carotene is consistent with the ineffective findings of the ATBC trial, the CARET trial, and the Physicians' Health Study. In 1983, a cancer chemoprevention study group was first established in Japan. Subsequently, (-)-epigallocatechin gallate, cryptoporic acid E, and sarcophytol A from natural products, and synthetic acyclic retinoid and canventol were shown to be anticarcinogenic or chemopreventive in human subjects. Despite the frequent consumption of tea wordwide as a beverage and current experimental evidence of anticarcinogenesis, including controversial results of epidemiological studies, more systematic clinical trials for confirmation of preventive activity of tea against cancer are needed. Placebo-controlled intervention trials of dietary fiber are under study in Japan. In the past decade, new triterpenoids were isolated from various natural sources, and its biological activities were investigated in Asia. In the late 1970s a comprehensive chemoprevention program was established at the Institute of Materia Medica, Chinese Academy of Medical Sciences. Since then, many retinoid compounds have been synthesized and screened in the search for chemopreventive cancer agents. The National Cancer Institute (USA) and China are jointly engaged in the two-nutrition intervention in Linxian, China. The results of joint study of the general population and of dysplasia in China should stimulate further research to clarify the potential benefits of micronutrient supplements. We need to clarify if there is a connection between the lower rates of cancer mortality in Korea and the frequent consumption of anticarcinogenic vegetables or traditional foods, including ginseng and Ganoderma lucidum. The constituents of the nontoxic stable dietary products promise to be the future hope for conquering cancers in the coming years.