Planarians as a model system for in vivo tumorigenesis studies

Planarians can be used to devise whole-animal invertebrate bioassays for screening and as an adjunct to, or replacement for, mammalian tests. This paper proposes using planarians for in vivo tumorigenicity studies of pure compounds and complex environmental mixtures, and for mechanistic studies of tumorigenesis. To accomplish the first two stages of the bioassay validation process described by Balls et al. (1990, ATLA 18, 313-337), the literature on tumorigenicity tests with intact planarians is reviewed. Thirteen of 14 mammalian chemical carcinogens produced tumors (usually of undetermined pathohistology) in planarians. Polychlorinated biphenyls are mammalian carcinogens which are cotumorigens but not complete tumorigens in planaria. Data for other mammalian chemical carcinogens for which the planarian results are incomplete are also presented. Planarian tests using mammalian noncarcinogens, compounds which have not been tested for carcinogenicity in mammals, and radiation are also reviewed. The results indicate that both the specificity and the sensitivity of the planarian tumorigen bioassay are high. Furthermore, first-stage validation data indicate that intact planaria can be used as a developmental toxicity bioassay.