Endodermal sinus tumour of the ovary: a comparative light and electron microscopic study.

An endodermal sinus tumour of the ovary from a 12 year old girl is analysed light- and electron microscopically. The histological appearance is characterized by glandular-papillary structures and microcystic-reticular areas with inclusion of occasional endodermal sinuses. By electron microscopy immature and highly differentiated cells can be distinguished. In analogy to certain structures in the human yolk sac the most differentiated cells in the tumour are regarded as neoplastic endoderm. On the basis of transitional forms between immature and differentiated cells a development of the latter from the former is suggested. The cells in mesenchyme-like areas differ from those of solid and glandular parts merely in the degree of cytoplasmic differentiation but are otherwise believed to represent the same "cell line". In addition to other possible cell functions the cytoplasmic features of the differentiated cell indicates a protein synthesis and secretion. From our observations it is concluded that the endodermal sinus tumour originates from germ cells and differentiates into yolk sac endoderm. The ultrastructural differences between this tumour and clear cell carcinomas of the ovary are discussed.