Ovarian GCTs account for approximately 25 to 30% of all ovarian tumors. The classification of the World Health Organization recognizes several entities that roughly correspond to testicular GCTs (Table 4-2).
Most ovarian GCTs are classified as benign ter-atomas (dermoid cysts), which account for 95% of all ovarian GCTs.21 Most patients are younger than 30 years of age. In the first two decades, ovarian GCTs account for 60% of all ovarian tumors, one-third of which are malignant.40,41
Dysgerminoma is the ovarian equivalent of testicular seminoma. It accounts for 1% of all ovarian GCTs and for close to 50% of all ovarian malignant GCTs. Most of the tumors occur in the second and third decade of life and are rarely found in persons under the age of 10 years or over the age of 50 years. In 15% of cases, the tumors are bilateral.21
Microscopically, the tumor is composed of uniform, round, or polygonal cells with vesicular nuclei
*World Health Organization classification.
and clear cytoplasm. As in testicular seminomas, these cells are arranged into nests, sheets, or cords enclosed by fibrous septa containing lymphocytes. The septa may contain plasma cells, macrophages, and giant cells, arranged into granulomas in some cases. Scattered multinucleated syncytiotrophoblas-tic cells that stain with antibodies to hCG are found in 3% of tumors.21,40 In approximately 15% of tumors initially thought to represent dysgerminomas, additional examination may reveal components of other GCTs, such as EC or yolk sac tumor; accordingly, such tumors are classified as mixed GCTs.21
Immunohistochemically, dysgerminoma cells react positively with antibodies to PLAP and inhibin/activin but are usually unreactive with antibodies to keratins, EMA, and AFP.2142
Yolk sac tumors are rare malignant tumors, accounting for approximately 0.5% of all ovarian GCTs and 20% of all malignant ovarian GCTs.21,40,41 Most tumors are diagnosed in the immediate postpubertal period, the mean age of patients at diagnosis being 16 to 19 years.41 These tumors are almost invariably unilateral and large (> 15 cm in diameter) and have a ruptured surface in 30% of cases.21 The patient's blood typically contains AFP in high concentration.
Microscopically, yolk sac tumors of the ovary have the same features as testicular yolk sac tumors. Round hyaline globules are often evident in the extracellular spaces. AFP can be demonstrated in tumor cells. In about 15% of cases, the tumors contain elements of other GCTs, most often squamous epithelium from dermoid cysts.41
Ovarian ECs are equivalent to testicular ECs. Like the testicular tumors, ovarian ECs are composed exclusively of EC cells. Such tumors are extremely rare, and most tumors show some form of differentiation of EC cells into teratoma, yolk sac tumor, or choriocarcinoma. Such tumors are then classified as mixed GCTs, and the pathologist is expected to list the various components identified microscopically.
Table 4-2. CLASSIFICATION OF OVARIAN GERM CELL TUMORS*
Dysgerminoma Yolk sac tumor Embryonal carcinoma Polyembryoma Choriocarcinoma Teratoma Immature Mature Monodermal Mixed tumor
ECs and mixed GCTs are very rare. They typically occur in young girls and women in the age group of 4 to 28 years (median, 12 years).41 Microscopically, ovarian EC cells are identical to testicular EC cells. Mixed GCTs contain hCG-positive syncytiotrophoblastic cells, AFP-positive yolk sac tumor cells, and various somatic tissues of teratoma.
Polyembryomas are extremely rare malignant tumors composed of EC cells arranged into bodies that resemble early embryos. In addition to these embry-oid bodies, these tumors usually contain other mixed germ cell elements. The recent review by Jondle and colleagues43 shows that fewer than 15 polyembry-omas have been reported in the last 60 years since the first case was described by Peyron.
Choriocarcinomas are tumors showing trophoblastic differentiation. Pure nongestational choriocarcino-mas of the ovary are extremely rare but highly malignant.40,41 Microscopically, the tumors are composed of mononuclear cytotrophoblastic and multi-nucleated syncytiotrophoblastic cells. Tumors are typically unilateral, but the contralateral ovary may contain teratomas.44
Teratomas are tumors that are composed of somatic tissues arranged in a haphazard manner. Three forms of teratoma are recognized: (1) immature teratoma, (2) mature teratoma, and (3) monodermal teratoma. Teratomas account for 98% of all ovarian GCTs, and most of these (95%) are classified as mature teratomas.21 Teratomas are tumors of young women, most of whom are diagnosed before 30 years of age.
Immature teratomas make up 3% of all ovarian teratomas. Typically, they present as solid ovarian tumors in girls and young women under the age of 20 years. In addition to mature somatic tissues, these tumors invariably contain embryonic neuroectodermal structures (Figure 4-6) and/or glial tissue resembling brain tumors such as astrocytoma, glioblastoma multiforme, or ependymoma. Squamous epithelium of the dermoid cyst is found in about 20% of tumors.
Immature teratomas can be graded histologically by quantifying the amount of immature neural tissue in the tumor. Using this approach, these tumors can be classified as low grade or high grade.21 Low-grade tumors contain less than one low-magnification microscopic field in any one microscopic slide. High-grade tumors contain immature neuroepithelial tissue exceeding one lower-power microscopic field per slide. Extraovarian spread typically takes place in the form of peritoneal implantation of glial tissue. Other embryonic malignancies, such as rhabdomyosarcoma,45 may arise occasionally from immature teratomas.
Mature teratomas are cystic in 80% of cases (Figure 4-7) and solid in the remaining 20% of cases. Mature solid teratomas occur in younger women and must be distinguished from immature teratomas, with which they share many features. Cystic teratomas represent the most common ovarian GCT. These teratomas can be diagnosed during a woman's entire reproductive life and even after menopause.
Most teratomas involve only one ovary, but bilat-erality is found in about 15% of cases. Histologically, the solid teratomas are composed of various mature somatic tissues derived from all three embryonic germ layers. Glial and neural tissue may be prominent, but in contrast to immature teratomas, there are no embryonic neuroectodermal structures. Cystic teratomas are predominantly composed of skin and skin appendages, including hair and sebaceous glands. Teeth, neural tissue, retinal epithelium, many mesenchymal tissues (such as cartilage, bone, fat tissue, and muscles), and endodermal derivatives (such as bronchial and intestinal components) may be found. Thyroid tissue is the most common endocrine tissue found. Occasionally, teratomas may be associated with benign tumors such as Brenner tumor.46
Mature teratomas are benign tumors. In some cases, however, these tumors may undergo malignant transformation and give rise to carcinomas and sarcomas. The most common malignant tumors originating in cystic teratomas are squamous cell carcinomas.21 Melanomas and sarcomas also may arise from these tumors.2147
Monodermal teratomas are composed almost exclusively of a single tissue and include entities such as struma ovarii, carcinoid tumors, and the neuroectoder-mal tumors, including ependymoma, neuroblastoma, medulloblastoma, and glioblastoma multiforme.40,41
Struma ovarii, composed of thyroid tissue, represents the most common monodermal teratoma (Figure 4-8). These tumors are usually solid but may be cystic, and they are often confused with other ovarian tumors.48 Tumors may be composed of typical thyroid tissue or may resemble thyroid only superficially (see Figure 4-8). Occasionally, struma may recur many years after the removal of the original tumor, even though the tumor appeared histologi-cally benign. Peritoneal implants (strumosis peri-tonei) are a rare complication.
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