Primary Prostatic Carcinoma with Metastasis to Epaxial Muscles and Myocardium in a Dog.

Canine prostatic carcinoma is a highly aggressive neoplasm with a strong tendency to metastasize, most commonly to regional lymph nodes, lungs, and bones. However, skeletal muscle and myocardial involvement are rarely reported. This report describes an 11-year-old intact male Maltese dog with a two-month history of anorexia and lethargy, referred for further evaluation after failing to respond to piroxicam therapy. Diagnostic imaging revealed a prostatic mass and multiple rim-enhancing lesions in the epaxial musculature and left ventricular wall, without evidence of metastasis to the lymph nodes, lungs, or other visceral organs. Hemostatic analysis indicated a hypercoagulable state. Postmortem examination confirmed metastatic prostatic carcinoma involving the semispinalis, multifidus, and myocardium. Histologically, the neoplastic cells exhibited similar morphology at the primary and metastatic sites. Immunohistochemistry revealed strong cytokeratin expression and absence of uroplakin III, consistent with a non-urothelial epithelial origin. No evidence of lymphatic involvement was observed. To the best of our knowledge, this is the first documented case of canine prostatic carcinoma with exclusive myotropic and myocardial metastases. These findings suggest a possible hematogenous metastatic route and highlight the importance of including muscle and cardiac tissues in staging protocols for canine prostatic carcinoma, even when lymphadenopathy or pulmonary lesions are absent.