Exceptional occurrence and extent of malignant melanoma in pig

Veterinarni Medicina 43, 1998, 87-91

The hereditary malignant melanoma (melanoblastoma) was recognised in a herd of miniature laboratory pigs kept at the Institute of Animal Physiology and Genetics, Academy of Sciences of the Czech Republic. These pigs genetically came from the original Hormel strain imported from the USA in 1967. Due to blood group studies, they were crossed with several other breeds and strains (Gottingen miniature pig strain, Canadian Landrace, Cornwall, Vietnamese pigs) during the past time. Selective breeding of animals bearing exophytic form of melanoma suggested a genetic basis to this disease. Mating of halfsiblings, which have been healed of tumours by surgical ischaemization (devitalization), proved a simple genetic predisposition. The segregation of tuberonodular form of melanoma in these families showed a simple mendelian character (1 : 1). The fast growth phase after birth, strong agressivity and severity of the tumour in some animals could be explained by matings of related parents and generally by inbreeding in our miniature pig line (F = 0.30). In one case, we observed an exceptionally large tumour and broad dissemination of the primary skin tumours. Metastatic lesions were greater in size and extent in comparison with cases published previously. The case report of this tumour is documented morphologically and histologically. The piglet with this tumour was strongly wasted and died at the 81st day after birth due to massive embolization of the arteria pulmonalis (sudden respiratory distress and dyspnoea). The two largest primary tuberonodular exophytic tumours (9 x 6 cm and 2.5 x 2.5 cm) were prominently elevated on the skin. Metastases were broadly disseminated in various organs and tissues: lungs, liver, gall-bladder, spleen, kidneys, adrenals, urinary-bladder, uterus, ovaries, pancreas, thymus, lymph nodes, thyroid gland and all segments of digestive tract including rectum. Great size and unusual locations of metastases were observed in organs where their occurrence in people or animal models is very rare or still has not been described (heart, diaphragm, aorta). Light microscopy confirmed the direct macroscopic examination and suggested that the histopathological features of the tumour are similar to human melanoma

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