Types of Ovarian Cancer
Ovarian cancer is not a single disease. There are actually more than 30 types and subtypes of ovarian malignancies, each with its own histopathologic (diseased tissue) appearance and biologic behavior. Because of this, most experts group ovarian cancers within three major categories, according to the kind of cells from which they were formed:
- epithelial tumors arise from cells that line or cover the ovaries;
- germ cell tumors originate from cells that are destined to form eggs within the ovaries; and
- sex cord-stromal cell tumors begin in the connective cells that hold the ovaries together and produce female hormones.
In addition, some tumors that are adjacent to ovarian tissues may be viewed as ovarian cancer. For example, extraovarian peritoneal carcinoma (intraperitoneal carcinomatosis)cancer of the membrane lining the walls of the pelvic cavity next to the ovariesis a tumor that is thought of and treated as if it were avanced ovarian cancer. The prognosis, or probable outcome of the disease, in patients with this condition is not very different from that in women with advanced ovarian carcinoma.
Common Epithelial Tumors
Common epithelial tumors begin in the surface epithelium of the ovaries and account for about 90 percent of all ovarian cancers. They are divided into a number of subtypesincluding serous, endometrioid, mucinous, and clear cell tumorsthat can be further classified as benign (noncancerous) or malignant (cancerous) tumors.
- Serous tumors are the most widespread forms of ovarian cancer. They account for 40 percent of common epithelial tumors. About 50 percent of these tumors are malignant, 33 percent are benign, and 17 percent are of borderline malignancy. Serous tumors occur most often in women who are between 40 and 60 years of age.
- Endometrioid tumors represent approximately 20 percent of common epithelial tumors. In about 20 percent of women, these cancers are associated with endometrial carcinoma (cancer of the womb lining). In 5 percent of cases, they also are linked with endometriosis, an abnormal occurrence of endometrium (womb lining tissue) within the pelvic cavity. The majority (about 80 percent) of these tumors are malignant, and the remainder (roughly 20 percent) usually are of borderline malignancy. Endometrioid tumors occur primarily in women who are between 50 and 70 years of age.
- Mucinous tumors make up about 1 percent of all common epithelial tumors. Most (approximately 80 percent) of these tumors are benign, 15 percent are of borderline malignancy, and only 5 percent are malignant. Mucinous tumors appear most often in women between 30 to 50 years of age.
- Clear cell tumors account for about 6 percent of common epithelial tumors. Nearly all of these tumors are malignant. Approximately one-half of all clear cell tumors are associated with endometriosis. Most patients with clear cell tumors are between 40 and 80 years of age.
Rare Types of Ovarian Tumors
In addition to the above, rare tumor types such as Brenner tumors, undifferentiated tumors, and transitional cell tumors also are seen.
- Brenner tumors, which comprise roughly 2 to 5 percent of epithelial tumors, are largely noncancerous tumors.
- Undifferentiated tumors are epithelial tumors with "primitive," unspecialized characteristics. The cells in such tumors are difficult to identify microscopically. Roughly 15 percent of all common epithelial tumors are undifferentiated tumors. Undifferentiated carcinomas are high-grade, solid tumors.
- Transitional cell tumors are generally high-grade (poorly differentiated, more malignant) tumors. Tumors that have primarily a transitional cell carcinoma pattern may have a better response to traditional chemotherapy than papillary serous carcinomas.
- Borderline ovarian tumors occur in 10 to 15 percent of cases. They have a low potential for malignancy, although they may be composed of a serous, endometrioid, mucinous, or clear cells. Borderline tumors generally arise on the ovarian surface and do not invade the ovary itself. For this reason, borderline tumors often have a better outcome than invasive ovarian tumors.
Endometrioid, clear-cell, and mucinous tumors often are low-stage lesions, whereas serous, transitional, and undifferentiated tumors tend to be high-stage lesions.
Germ Cell Tumors
Germ cell tumors are formed from egg-making cells within the ovaries. They represent approximately 3 percent of all ovarian cancers in Western countries. Germ cell tumors tend to occur in young women, with a peak incidence among individuals who are in their early 20s. Like testicular cancer, these tumors usually are very curable. In addition, they are associated with specific markers (proteins) that are released into the blood, such as beta-human chorionic gonadotropin (ß-HCG) and alpha fetoprotein (AFP). After germ cell tumors have been treated, the physician may conduct blood tests for ß-HCG and/or AFP, to determine whether the cancer is recurring (returning).
Unlike patients with common epithelial tumors, 75 percent of whom are Stage 3 or 4 at diagnosis, between 60 and 70 percent of patients with germ cell tumors are Stage 1; most remaining patients are Stage 3 (Stages 2 is relatively rare for this tumor type).
Germ cell tumors are divided into dysgerminomas and nondysgerminomatous types.
- Dysgerminoma is the most common germ cell tumor, representing nearly one-half of all cases. This tumor has been likened to the male testicular cancer known as seminoma. A vast majority (some 80 percent) of dysgerminomas affect women younger than 30, and roughly 20 percent of such tumors are diagnosed during pregnancy.
- Nondysgerminomatous tumors are less common than dysgerminomas. Tumors in this category include embryonal carcinoma, a very malignant, primitive form of carcinoma; immature teratoma, a tumor made up of different tissues that are not normally found in the ovary; choriocarcinoma, malignant tumor of the placental epithelium; polyembryoma, a tumor formed from embryonic cells; and mixed germ cell tumors, tumors containing a variety of cell types.
Sex Cord-Stromal Tumors
Sex cord-stromal tumors represent about 5 percent of all ovarian cancers. They are formed from cells of the sex cord or mesenchyme (early connective tissue) within the embryonic gonad, and they may contain gonad-related cells (e.g., granulosa cells, Sertoli cells, thecal cells) as well as fibroblasts, which are immature, connective tissue-forming cells. The most common tumors in this category are granulosa stromal cell tumors and Sertoli- or Sertoli-Leydig cell tumors; other related tumors include lipid cell tumors and gynandroblastomas.
Granulosa stromal cell tumor is the most prevalent tumor in this category. It is more common in postmenopausal women, and it may produce symptoms such as vaginal bleeding and an elevated blood level of the tumor marker inhibin, a peptide hormone that prevents the release of follicle stimulating hormone (FSH). Perhaps because of this, individuals who have granulosa cell tumors often are diagnosed at an early stage.
Sertoli and Sertoli-Leydig cell tumors are very rare. Most patients with these tumors are young; the average age is 25 years, with only 10 percent of individuals being over age 50. Pure Sertoli cell tumors and pure Leydig cell tumors are benign; however, their malignant potential is determined by their grade (see also Tumor Grade). Well-differentiated Sertoli-Leydig tumors usually behave in a benign manner, whereas poorly differentiated tumors tend to be malignant.
In general, sex cord-stromal tumors are associated with hormonal effects such as virilization, the development of male secondary sex characteristics (e.g., a low voice, facial hair); precocious puberty, early sexual maturity; amenorrhea, absence/stopping of the menstrual period; or postmenopausal bleeding.