Malignant cutaneous neoplasms arise in the newt, Triturus cristatus Laur., as a result of treatment with chemical carcinogens. The architecture of the tumor and features of early lesions support the idea that the tumor arises by a multicentric proliferation of the melanocyte system and can be classified as scanty pigmented melanoma, usually associated with junctional activity (Pl. I-II). Electron microscopy shows that neoplastic cells contain melanin and premelanin granules which occur in various amounts and degree of melanization (Pl. III). The DOPA-oxydase histochemical reaction varied according to individual cases, while tyrosinase reaction was negative. The tumor has been successfully transplanted into animals of the same species and of different genus or even order, without conditioning the recipient animals. The growth rate of the tumor is greatly dependent on the environmental temperature: it is drastically retarded at 4°C, whereas massive widespread metastases develop in animals maintained at 30°C, with a survival rate of 15-20 days. Various studies carried out in our laboratory aimed first at gaining experimental evidence of a viral etiology. Towards this end, two different experiments were devised, one consisting of the treatment of the animals with cell-free ultrafiltrates of the tumor, the other consisting of the treatment of the animals with nucleic acids extracted from the tumor; control animal were injected with preparations of normal organs. In the 254 animals injected with ultrafiltrates a rough correlation has been observed between the incidence of the melanoma and the spreading of the tumor in the donors (Table I) (however these results must be looked at with some caution, because virus-like particles have never been found in electron microscope studies). Such a correlation has not been demonstrated in the 670 newts injected with nucleic acids: of interest is the fact that, in this experimental group, the overall incidence of melanoma was very high in animals coming from areas with high industrialization, i.e. in the newts from the environs of Pavia (54%) in comparison with the newts from Napoli (11%): the difference was highly significant (P < 0.001) and independent of the treatment. As nothing is known about the natural history of the melanoma of the newt, an epidemiological study has been undertaken. We have examined 909 animals caught in minimally polluted waters of the environs of Milano (Rosate: 416 cases) and of the environs of Perugia (Bagnaia: 494 cases) in order to study the prevalence rate of the tumor in natural populations of different geographical origin. Twelve tumors (2.9%) were found in the newts collected in the neighbourhood of Rosate, while in the animals from Perugia, the tumor rate was lower (0.8%). No relationship between body length and tumor rate has been observed (Table II). Further research is envisaged to study the influence of water pollution on melanoma prevalence.
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Con il contributo del Ministero per i Beni e le Attività Culturali