Professional Phagocytes-Mediated Partial Spontaneous Regression of Congenital Cardiac Rhabdomyoma in a Litter of Pigs

Familial incidence of congenital cardiac rhabdomyoma was observed in a litter of pigs (four 6-month-old castrated males) that were conventionally slaughtered for food. The hearts of these pigs were found to have multiple tumour nodules in the left ventricular free wall and interventricular septum. Histopathology revealed the tumours to be comprised of large neoplastic cells that had myofibril-like structures with crossstriations and variable numbers of glycogen-containing vacuoles, representing a rhabdomyomatous appearance. The neoplastic cells were considered to be of cardiac myocyte origin, dislpaying positive immunohistochemical labelling for desmin and vimentin and negative labelling for neuron-specific enolase and protein gene product 9.5. Occasional tumours smaller in size than others exhibited partial spontaneous regression, characterized by atrophic or degenerated neoplastic cells associated with fibrosis and infiltration of professional phagocytes, including eosinophils, macrophages and multinucleated giant cells. The professional phagocytesmediated immunity was considered likely to be involved in partial spontaneous regression of cardiac rhabdomyoma in these juvenile pigs. These swine cases would serve as a useful animal model for understanding morphological changes in spontaneous regression of human cardiac rhabdomyoma.