MIXED TUMORS WITH FOLLICULAR DIFFERENTIATION: COMPLEX NEOPLASMS OF THE PRIMARY EPITHELIAL GERM

Abstract

Some mixed tumors of the apocrine variety also show characteristics of follicular and/or sebaceous differentiation. This can be explained because of the common embryologic origin of the three structures in the primary epithelial germ of the superficial ectoderm.Twenty specimens of apocrine mixed tumors were studied by conventional microscopy. The specimens were evaluated searching for some features of folliculo-sebaceous differentiation.Certain features of folliculo-sebaceous differentiation were found in 45% of the samples examined. Additionally, different tumoral architectures were observed, resembling several well-characterized adnexal organoid neoplasms. In some tumors, there were also follicular structures of mesenchymal origin, similar to the dermal hair papilla and the arrector pili muscle.Apocrine mixed tumors of the skin illustrate the ability of pluripotential primordial cells to differentiate in different directions within an individual tumor. Moreover, mixed tumors appear as a compendium of different folliculo-sebaceous neoplasms. We suggest that these proliferations should be interpreted as "complex neoplasms of the primary epithelial germ."