There are more than 30 different types of ovarian cancer, which are classified by the type of cell from which they start. Cancerous ovarian tumors start from three common cell types
Types of Ovarian Cancer
Surface Epithelium – cells covering the outer lining of the ovaries
Germ Cells – cells that are destined to form eggs
Stromal Cells – Cells that release hormones and connect the different structures of the ovaries
Epithelial Tumors – Epithelial ovarian tumors develop from the cells that cover the outer surface of the ovary. Most epithelial ovarian tumors are benign (noncancerous). There are several types of benign epithelial tumors, including serous adenomas, mucinous adenomas, and Brenner tumors. Cancerous epithelial tumors are carcinomas – meaning they begin in the tissue that lines the ovaries.
These are the most common and most dangerous of all types of ovarian cancers, accounting for 85 to 90 percent of all cancers of the ovaries. Unfortunately, almost 70 percent of women with the common epithelial ovarian cancer are not diagnosed until the disease is advanced in stage.
There are some ovarian epithelial tumors whose appearance under the microscope does not clearly identify them as cancerous. These are called borderline tumors or tumors of low malignant potential (LMP tumors).
Germ Cell Tumors – Ovarian germ cell tumors develop from the cells that produce the ova or eggs. Most germ cell tumors are benign (non-cancerous), although some are cancerous and may be life-threatening. The most common germ cell malignancies are maturing teratomas, dysgerminomas, and endodermal sinus tumors. Germ cell malignancies occur most often in teenagers and women in their twenties. Today, 90 percent of patients with ovarian germ cell malignancies can be cured and their fertility preserved.
Stromal Tumors – Ovarian stromal tumors are a rare class of tumors that develop from connective tissue cells that hold the ovary together and those that produce the female hormones, estrogen and progesterone. The most common types are granulosa-theca tumors and Sertoli-Leydig cell tumors.
These tumors are quite rare and are usually considered low-grade cancers, with approximately 70 percent presenting as Stage I disease (cancer is limited to one or both ovaries). Granulosa cell tumors (GCTs) are considered stromal tumors and include those composed of granulosa cells, theca cells, and fibroblasts. GCTs account for approximately 2 percent of all ovarian tumors.
Primary Peritoneal Carcinoma
The removal of one’s ovaries eliminates the risk for ovarian cancer, but not the risk for a less common cancer called Primary Peritoneal Carcinoma. Primary Peritoneal Carcinoma is closely related to epithelial ovarian cancer, which is the most common type. It develops in cells from the peritoneum (abdominal lining) and looks the same under a microscope. It is similar in symptoms, spread, and treatment.
Stages of Ovarian Cancer
Once diagnosed with ovarian cancer, the stage of a tumor can be determined during surgery, when the doctor can tell if the cancer has spread outside the ovaries. There are four stages of ovarian cancer – Stage I (early disease) to Stage IV (advanced disease). The treatment plan and prognosis (the probable course and outcome of the disease) will be determined by the stage of the cancer.
Grades of Ovarian Cancer
Tumor grade is not the same as the cancer stage. Grade (G), describes how healthy the cancer cells look when viewed under a microscope. The doctor compares the cancerous tissue with healthy tissue. Healthy tissue is made up of many types of cells grouped together. If the cancer looks like the healthy tissue with different cell groupings, it is called differentiated or a low-grade tumor. If the tissue looks very different, it is called poorly differentiated or a high-grade tumor. The cancer’s grade may help the doctor predict how quickly the cancer will spread. It also helps determine a treatment plan decision.
The following is a description of tumor grades:
GX: The grade cannot be evaluated
GB: The tissue is considered borderline cancerous. This is commonly called low malignant potential (LPM).
G1: The tissue is well-differentiated (contains many healthy looking cells)
G2: The tissue is moderately differentiated (more cells appear abnormal than healthy)
G3 to G4: The tissue is poorly differentiated or undifferentiated (more cells appear abnormal, and lack normal tissue structures)