Cancer in Amphibia, a rare phenomenon?

Compared to other animals, the spontaneous occurrence of tumors in wild amphibians is relatively rare, generally limited to specific populations or species. The number of reports of spontaneous tumors in amphibians known up to 1986 was 491 cases in anurans and about 253 cases in urodeles. Similarly, there have been many, unsuccessful attempts to chemically or biologically induce tumors in amphibians. With these considerations, it is inevitable to wonder: do urodeles and anurans have an inherent resistance to cancer? Here, we review the spontaneous and induced occurrence of tumors in amphibians in a timeline, as well as failed attempts to induce tumors in these amphibians. Indeed, recent studies seem to indicate that there is a relationship between regeneration and cancer because regenerating tissues seem to resist tumorigenesis, as opposed to nonregenerative tissues of the same amphibian models. Although the mechanisms that allow regenerating tissues to resist tumorigenesis have not been elucidated, it is worth to note that, in addition to the apparent relationship between regeneration and cancer, amphibians possess characteristics that could contribute to their ability to resist the development of neoplastic events. The implications of these features in cancer susceptibility are discussed.