Morphopathological study of naturally occurring ovine pulmonary adenocarcinoma in sheep in Fars province, Iran

Ovine pulmonary adenocarcinoma (OPA) is a contagious and transmissible lung cancer of sheep resembling human bronchiolo-alveolar carcinoma. In the present study, lungs of 9400 sheep slaughtered in Fars province, Iran were examined morphopathologically. The OPA was diagnosed in the lungs of 21 (0.22%) out of 9400 sheep. Frequency of involvement of different lobes in the affected lungs was included apical lobe (62%), cardiac lobe (33%), middle lobe (33%), diaphragmatic lobe (62%) and accessory lobe (5%). In 12 sheep, the classical form observed as firm, white to grayish coalescing masses mostly in the cranio-ventral lobes associated with wet cut surface and frothy fluid in the airways. In 9 sheep, atypical lesions observed as small clearly demarcated nodules mostly in diaphragmatic lobes associated with dry cut surface and minor fluid in the airways. Histopathological changes were almost similar in the two forms. They consisted of an acinar or papillary growth of neoplastic cells in the alveoli and polypoid proliferation of bronchiolar epithelium. There were variable amounts of connective tissue, myxomatous foci and infiltration of lymphocytes and plasma cells in the interstitial tissue of the affected alveoli. No metastatic lesion was observed in the lymph nodes. The findings of this study show that atypical and classical forms represent different stages or manifestations of a single disease spectrum.