BOVINE PULMONARY BLASTOMAS - HISTOMORPHOLOGIC DESCRIPTION AND IMMUNOHISTOCHEMISTRY

Three adult female dairy cattle with pulmonary blastomas were evaluate d. The gross lesions at postmortem were described as multiple white ci rcumscribed masses throughout the lungs, with pleural involvement in o ne cow and lymph node metastasis in the other two cows. Histologically , the tumors contained a dual population of mesenchymal and epithelial neoplastic cells. Epithelial cells formed nests, tubules, and formati ons resembling bronchioles of normal lung. Mesenchymal cells were spin dle shaped with oval nuclei and fibrillar eosinophilic cytoplasm, were large rounded cells with multiple round nuclei and granular eosinophi lic cytoplasm, or appeared blast-like, with large hyperchromatic nucle i and amphophilic cytoplasm. The tumors varied greatly in appearance f rom one field to another within the same tumor. Epithelial cells stain ed positively with anti-cytokeratin antibodies. Some spindle-shaped me senchymal cells exhibited smooth muscle cell differentiation with posi tive staining with anti-vimentin, anti-muscle-specific actin, and anti -smooth muscle actin antibodies, whereas other rounded mesenchymal cel ls expressed striated muscle cell differentiation with multiple nuclei and positivity to anti-neuron-specific enolase and anti-muscle-specif ic actin antibodies. The variable expression of the intermediate filam ents and cytoplasmic enzymes indicates multiple pathways of differenti ation in the pulmonary blastomas.