The role of myoepithelial cells in the morphogenesis of induced mammary tumours.

The localization and cytomorphology of myoepithelial (ME) cells and their role in the morphogenesis of the mammary gland tumours of Wistar rats induced by 7,12-Dimethylbenz-a-anthracene-DMBA- were studied. Cells which do not participate in secretion and contain cytoplasmic myofibrillar bundles in a typical arrangement are considered to be of ME origin. In the histogenesis of induced mammary gland tumours no difinite role can be attributed to mature ME cells or their precursors. Decreased differentiation is associated with reduced numbers of ME cells. No ME cells can be detected in the anaplastic, stromafree portions of the solid tumour. The sarcomatous component of the induced carcinosarcomas originates from connective tissue. ME cells may give rise to leiomyoma-like tumours comparable with the human benign mammary myoepithelioma. The atrophic areas of mammary gland tumours consisted mostly of preserved ME cells. The ME cells of induced mammary gland tumours were, in every respect, identical with the normal ME cells of control mammary glands.