Spontaneous thyroid-containing teratoma associated with impaired development in the African clawed frog, Xenopus laevis

Teratomas are rare in amphibians and the neoplasm described here, which had a significant thyroid carcinoma component, is the first tumour of this type to be reported in Xenopus laevis. The thyroid component contained moderately to well-differentiated acinar glands showing much hyperplasia, dysplasia, and reduced and distorted colloid reservoirs. Cartilaginous, neural, muscular, mesenchymal and gut-like epithelial components were also observed in this ventral mediastinal neoplasm, indicating aberrant proliferation from all three germ layers. This teratoma was only one abnormality in a complex of developmental changes, followed for 28 months, which appeared in a single generation of sibling 2-week-old Xenopus larvae. Two hundred larvae produced by an apparently normal adult pair initially showed ocular defects, including microphthalmia, anophthalmia and tumours projecting near the eyes. During further development up to 28 months, mediastinal tumours developed in nine frogs; these tumours were associated with reduced growth, the frogs reaching only 13-20% of normal weight, and greatly enhanced ventral pigmentation.