RESUMEN
A 74-year-old woman was admitted in a serious condition due to the failing right heart. A CT scan revealed a tumor infiltration through the interventricular septum in the right heart, spreading from the apex as far as under the tricuspid valve. The tumor penetrated into the conus of the pulmonary artery, bulging and markedly narrowing the lumen. As a result of the tumor infiltration, the patient died from cardiac failure. Histological examination of the tumor revealed atypical elongated cells and areas of large cells with significantly enlarged hyperchromatic and lobulated nuclei. In some portions, the tumors had a biphasic appearance. The tumor cells resembled epithelial tissue but immunohistological analyses to detect cytokeratins yielded negative results. The elongated cells expressed desmin and smooth muscle actin. A vast majority of the tumor was solid or hard, histologically corresponding to osteosarcoma. Later, it was found that the patient undergone right-sided mastectomy for a malignant phyllodes tumor with osteosarcomatous differentiation three years previously. The metastasis to the heart was the only metastasis detected by the autopsy.