Synaptophysin and/or chromogranin A may be expressed in epithelial cells of normal and dysplastic mammary gland and in some cancer of the breast. This work indicates that some stromal cells form thin walled vascular channels and from their perivascular mesenchyma arise myoid-like cells, some with cross-like striations. These myoid-like cells have been stained with antibody to smooth muscle actin, rarely to desmin and sarcomeric actin as well as are strongly positive for synaptophysin and/or chromogranin A. From those cells arise cancer cells. Some cancer cells also expressed desmin, sarcomeric actin or smooth muscle actin. Because synaptophysin positive are neuromuscular endplates, it is a question whether the presence of synaptophysin in the progenitor of neoplastic cells of myogenic origin is due to the synaptic dysfunction in molecular mechanism of the epithelial-parenchyma and mesenchymal stroma interaction. The location of S100-protein positive dendritic cells distributed in regular pattern in suprabasal layer of the mammary gland indicate that these cells may arise from preadipocytes which take part in morphogenesis of the breast. All cases of the breast cancer demonstrated thymosin alpha 1, some of them also showed Hassall's-like bodies, mucin secretion and minute calcification. Whether the interaction of epithelial cells and S100-protein positive dendritic cells in tissue other than the thymus has similar dynamic activity to that of Hassall's bodies of the thymus remains to be determined. Both, epithelial cells of Hassall's bodies and epithelial cells of the investigated breast are of myogenic origin. The above consideration suggests that the cells forming vascular channels are with a differentiation defect as they are created in altered stromal mesenchyma and the presence of thymic growth factors might induce tumor growth.