Ovarian yolk sac carcinoma in mice.

Abstract

Ovarian yolk sac carcinoma or endodermal sinus tumor is a rare neoplasm of germ cell origin. The rodent yolk sac is composed of visceral and parietal layers, contained by a thick basement membrane (Reichert’s membrane), which is secreted by the cells of the parietal la~er.~.~ The parietal yolk sac cells are small cuboidal cells with relatively large centrally placed nuclei6 External to Reichert’s membrane is a layer of trophoblastic giant cell^.^,^ Neither the parietal yolk sac cells nor the tumors derived from them secrete alphafetoproteh8 The human yolk sac does not have two distinct cell types and there is no counterpart of Reichert’s membrane; consequently, yolk sac tumors of humans differ in appearance.* In man, these neoplasms are found in ovaries, testis, and a variety of extragonadal sites, and they secrete alphafetoprotein.’ Yolk sac carcinoma may be induced in rats by transplantation of the extraembryonic portion of the 8-9-day-old egg or by fetectomy without removal of the fetal membranes.’ It has been produced experimentally in mice by serial passaging and conversion to ascitic form of testicular4 and ovarian5 teratocarcinomas, by transplantation of embryos without extraembryonic tissues under the kidney capsule of adult mice,2 and more recently by fetectomy and displacement of the visceral yolk sac to an extrauterine site.’ Spontaneous yolk sac carcinoma appears to be rare in mice,8 and the authors are aware of only one spontaneous case of pnmary ovarian yolk sac carcinoma.) The purpose of this paper is to document and describe the appearance of 16 ovarian yolk sac carcinomas found in one CD 1 and 15 B6C3F1 mice from chronic carcinogenesis studies. Seven of the 16 mice were control animals, the remainder were treated animals from different studies. The ages of the mice at necropsy ranged from 34 to 106 weeks, with a mean age of 66 weeks. The tumors were found during post-mortem examination of the abdominal cavity. They were unilateral, dark, gelatinous or cystic masses up to 25 millimeters in diameter, replacing the ovary and ovarian bursa, and attached to the uterine horn. The cystic spaces within the neoplasms contained serosanguinous fluid. The tumors were characterized histologically by a copious hyaline, periodic acid-Schiff (PAS) positive matrix in which the neoplastic cells were embedded. This intercellular matrix stained positively for laminin (Gibco Laboratories Inc., Grand Island, NY) using an immunogold method (Janssen Life Sciences Products, Piscataway, NJ) (Fig. 3). Areas of fine fibrovascular tissue, hemorrhage, and macrophages loaded with fine brown granules characteristic of hemosiderin were present in many sections.