Histology and immunohistochemistry of canine cardiac rhabdomyosarcoma.

Primary cardiac rhabdomyosarcoma is extremely rare in the dog. The only gross lesion detected in a five year old male, German short-hired pointer that had died suddenly was a white swelling in the right ventricular wall. Coronal cuts from the apex to the base of the heart revealed light-gray tissue more evident in the septum, which was uniformly involved. Histologically, the tumour consisted of both oval cells with scanty cytoplasm and triangular cells with abundant cytoplasm. Neoplastic cells disrupted the myofibers. Numerous mytotic figures were also seen. Immunohistochemistry was positive for desmin antigen, expecially in a lung micrometastasis in which immunoreactivity for alfa-actinin in its characteristic cross-striation was also present in scattered neoplastic cells