A case of two different tumors in the heart of a dog.

A 9-year-old, spayed, female Maremmano shepherd had a bilateral mastectomy for multiple mammary adenocarcinomas 2 years previous and was referred to the Cardiology Service of the School of Veterinary Medicine of Milan after an acute episode of cardiogenic collapse. Because of severe cardiovascular symptoms and poor prognosis, the dog was euthanized. Necropsy examination revealed the presence of multiple firm grayish neoplastic nodules in the myocardium of the left ventricle and scattered in the pulmonary parenchyma. Neoplastic nodules were also detected in the spleen, pancreas, liver, kidneys, and omentum. Histological examination revealed the coexistence of tubular adenocarcinoma and an undifferentiated sarcoma in the myocardium. Immunohistochemical staining of the sarcoma cells was negative for cytokeratin, desmin, and smooth muscle myosin, thus excluding their epithelial or myoepithelial origin, as well as an origin from smooth muscles cells. These findings, together with the coexpression of vimentin and alpha-smooth muscle actin, suggested that the sarcoma was derived from myofibroblasts. To the authors' knowledge, this is the first report describing cardiac sarcoma of presumptive myofibroblastic origin in a dog with simultaneous occurrence of cardiac metastasis of mammary gland adenocarcinoma.