Spontaneous hepatocellular and gastric tumours in African clawed frogs (Xenopus laevis)

Three seven-year-old African clawed frogs (Xenopus laevis) from an animal research facility showed weight loss, coelomic distention and an abnormal swimming gait were euthanised on welfare grounds. A complete necropsy of each animal showed a focal, firm, dark brown to green mass with multifocal haemorrhages in the left liver lobe in two animals and a transmural, firm, beige, multilobulated gastric mass in another animal. Additionally, one of the frogs with the hepatic mass had haemocoeloma. Histologically, the hepatic masses were diagnosed as hepatocellular adenomas and the gastric mass as a gastric carcinoma with trans-coelomic metastases. The three tumours were immunophenotyped using the following antibodies: cytokeratin AE1/AE3, vimentin, E-cadherin, P53 and Ki67 and, additionally, for the hepatic tumours only, synaptophysin, Prox-1, S100 and Sox-9. Masson's trichrome, Periodic acid Schiff and Gram stains was also performed in selected cases. One of the hepatocellular adenomas was weakly positively labelled with E-cadherin whereas the other showed variable positivity for Sox-9 only. Vimentin labelled the stroma and sinusoidal endothelia. Interestingly in the liver, the cytokeratin AE1/AE3 labelling was restricted to the biliary epithelium and sinusoidal endothelia. The gastric carcinoma labelled positively with cytokeratin AE1/AE3 only. This report aims to guide laboratory animal veterinarians to accurately diagnose multi-organ masses in amphibians. To the authors' knowledge, this is the first comprehensive morphological study on a case series of hepatocellular and gastric neoplasia in X. laevis.