[Phenotypic heterogeneity of cardiac myxomas]

Histogenesis of cardiac myxoma is still unclear. Beside endothelial cells a variety of different cell types were detected in this benign cardiac tumor. Cryostat sections of four myxomas were analysed in the indirect immunoperoxidase technique using monoclonal antibodies (MoABs) directed against MHC class I and II antigens, as well as different surface determinants specific for endothelial cells or monocytes/macrophages. Tumor cells forming cell clusters and blood vessel like structures differed in their expression of endothelial antigens suggesting cellular heterogeneity within single and different myxomas. Like in fetal cardiac tissue vascular channels rarely carried HLA-class II antigens. Tumor cells carrying antigens of monocytes/macrophages, as well as intracellular alkaline phosphatase of endothelial cells could represent subpopulations of an early differentiation stage. This analysis further supports previous hypothesis of an endothelial origin of myxomas.