Surface active agents as tumor promoters.

Although physical injury was the first type of tumor promoter to be described (1) and croton oil with its constituents the most investigated, some of the other types of the fourteen listed in Table 1 are certainly involved as causes of human cancer. Some of the types of promoter listed have not been demonstrated as such by animal experiments, but if a substance is a carcinogenic but not mutagenic, then it is most probably a tumor promoter. This assumes that mutagens are initiators and that promoters can induce cancer because initiators are present in the diet or environment. Until recently, the adventitious initiators were considered as contaminants such as aflatoxin or nitrosamines, but the mutagen and carcinogen, quercitin, is present as such or as glycosides in most vegetable matter and in animal foods. Substances which inhibit DNA repair or suppress immune response might also increase cancer incidence and so be considered as carcinogens without being promoters. Some neoplasia including liver tumors in mice, bladder, kidney and thyroid tumors in rats are easily induced by promoters so that their occurrence is almost indicative of tumor promotion.Tumor promoters are organotropic and canchange the sit e of action of an initiator. Thus tryptophan can change the site of action of 2-acetylaminofluorene from the liver to the bladder and thiouracil from the liver to the thyroid. Some carcinogens, particularly aromatic amines, cause cancer in different organs in different species; this effect could be due to tumour promotion.