Cardiac myxoma: an immunoperoxidase study of histogenesis.

Eleven surgically excised left atrial myxomas have been stained for factor VIII related antigen (VIII-RA) and actin by the peroxidase-antiperoxidase technique. Most tumour cells were negative for VIII-RA. However a population was identified forming cords and vascular channels which possessed a core or lining of tumour cells with an endothelial morphology which were positive. Tumour cells lining vessel-like invaginations of the surface also showed focal positive staining. The staining pattern for actin precisely mirrored that for VIII-RA. These findings support the established theory that cardiac myxomas arise from primitive endocardial or subendocardial mesenchymal cells with the potential to differentiate towards endothelial cells. They are incompatible with the theory that these tumours originate from cardiac endothelium.