CELL RENEWAL, CELL-DIFFERENTIATION AND PROGRAMMED CELL-DEATH (APOPTOSIS) IN PILOMATRIXOMA

Pilomatrixoma is a benign tumour of the cutaneous adnexa. Histological ly, pilomatrixoma comprises masses of immature basophilic cells, small numbers of polygonal squamoid cells, few transitional cells. and clus ters of 'shadow cells'. The mechanism leading to the formation of shad ow cells is still unknown. Skin biopsy specimens of pilomatrixoma (n = 15) were studied histologically, immunohistologically, and by applyin g the in situ end-labelling technique, The basal layer of the basophil ic cells included most of the proliferating cells with high expression of bcl-2, and cytokeratin 19, The overlying basophilic cells showed a negligible mitotic activity, a high significant accumulation of p53 p rotein, and a heterogeneous, but progressive loss of bcl-2 and cytoker atin 19, They developed either into squamoid cells or into transitiona l cells. The squamoid cells were characterized as differentiated cells resembling mature keratinocytes of stratified mucosa, The transitiona l cells could be shown to represent apoptotic cells proceeding to shad ow cells. The data suggest that apoptosis is the main mechanism leadin g to the development of the dead shadow cells and is most probably res ponsible for the banal biological behaviour of pilomatrixoma. Apart fr om that, pilomatrixoma represents a suitable biological model to study apoptosis in humans.