The ovaries contain 3 kinds of tissue:

• Epithelial cells, which cover the ovary.  
• Germ cells are found inside the ovary. These cells develop into the eggs (ova) that are released into the fallopian tubes every month. 
• Stromal cells, which produce most of the female hormones estrogen and progesterone.

Types of ovarian tumors

Many types of tumors can start growing in the ovaries. Most of these are benign (non-cancerous) and never spread beyond the ovary. Benign tumors can be treated successfully by removing either the ovary or the part of the ovary that contains the tumor. Ovarian tumors that are not benign are malignant (cancerous) and can spread (metastasize) to other parts of the body. Their treatment is more complex and is discussed later in this document.

In general, ovarian tumors are named according to the kind of cells the tumor started from and whether the tumor is benign or cancerous. There are 3 main types of ovarian tumors:

• Epithelial tumors start from the cells that cover the outer surface of the ovary. Most ovarian tumors are epithelial cell tumors. 
• Germ cell tumors start from the cells that produce the ova (eggs). 
• Stromal tumors start from connective tissue cells that hold the ovary together and produce the female hormones estrogen and progesterone.

Epithelial ovarian tumors

Benign epithelial ovarian tumors: Most epithelial ovarian tumors are benign, do not spread, and usually do not lead to serious illness. There are several types of benign epithelial tumors including serous adenomas, mucinous adenomas, and Brenner tumors.

Tumors of low malignant potential: When looked at under the microscope, some ovarian epithelial tumors do not clearly appear to be cancerous. These are called tumors of low malignant potential (LMP tumors). They are also known as borderline epithelial ovarian cancer. These differ from typical ovarian cancers in that they do not grow into the supporting tissue of the ovary (called the ovarian stroma). Likewise, if they spread outside the ovary, for example, into the abdominal cavity, they do not usually grow into the lining of the abdomen.

These cancers tend to affect women at a younger age than the typical ovarian cancers. LMP tumors grow slowly and are less life-threatening than most ovarian cancers. Although they can be fatal, this is not common.

Malignant epithelial ovarian tumors: Cancerous epithelial tumors are called carcinomas. About 85% to 90% of ovarian cancers are epithelial ovarian carcinomas. When someone says that they had ovarian cancer, they usually mean that they had epithelial ovarian carcinoma. When these tumors are looked at under the microscope, the cells have several features that can be used to classify epithelial ovarian carcinomas into different types. The serous type is by far the most common, but there are other types called mucinous, endometrioid, and clear cell.

If the cells don't look like any of these 4 subtypes, the tumor is called undifferentiated. Undifferentiated epithelial ovarian carcinomas tend to grow and spread more quickly than the other types. In addition to being classified by these subtypes, epithelial ovarian carcinomas are also given a grade and a stage.

The grade classifies the tumor based on how much it looks like normal tissue on a scale of 1, 2, or 3. Grade 1 epithelial ovarian carcinomas look more like normal tissue and tend to have a better prognosis (outlook). Grade 3 epithelial ovarian carcinomas look less like normal tissue and usually have a worse outlook.

The tumor stage describes how far the tumor has spread from where it started in the ovary. Staging is explained in detail in a later section.

Primary peritoneal carcinoma

Primary peritoneal carcinoma (PPC) is a rare cancer closely related to epithelial ovarian cancer. At surgery, it looks the same as an epithelial ovarian cancer that has spread through the abdomen. Under a microscope, PPC also looks just like epithelial ovarian cancer. Other names for this cancer include extra-ovarian (meaning outside the ovary) primary peritoneal carcinoma (EOPPC) or serous surface papillary carcinoma. Primary peritoneal carcinoma develops in cells from the lining of the pelvis and abdomen (which is called the peritoneum). These cells are very similar to the cells on the surface of the ovaries. Like ovarian cancer, PPC tends to spread along the surfaces of the pelvis and abdomen, so it is often difficult to tell exactly where the cancer first started. This type of cancer can occur in women who still have their ovaries, but it is of more concern for women who have had their ovaries removed to prevent ovarian cancer.

Symptoms of PPC are similar to those of ovarian cancer, including abdominal pain or bloating, nausea, vomiting, indigestion, and a change in bowel habits. Also, like ovarian cancer, PPC may elevate the blood level of a tumor marker called CA-125.

Women with PPC usually get the same treatment as those with widespread ovarian cancer. This could include surgery to remove as much of the cancer as possible (this process is called debulking and is discussed in the Surgery section), followed by chemotherapy like that given for ovarian cancer. Its outlook is similar to widespread ovarian cancer.

Fallopian tube cancer

This is an extremely rare cancer. It begins in the tube that carries an egg from the ovary to the uterus (the fallopian tube). Like PPC, fallopian tube cancer causes symptoms similar to those seen in women with ovarian cancer. The treatment and outlook for survival (prognosis) is similar to that for ovarian cancer.

Germ cell tumors

Germ cells are the cells that usually form the ova or eggs. Most germ cell tumors are benign, although some are cancerous and may be life threatening. About 5% of ovarian cancers are germ cell tumors. There are several subtypes of germ cell tumors. The most common germ cell tumors are teratoma, dysgerminoma, endodermal sinus tumor, and choriocarcinoma.

Teratoma

Teratomas are germ cell tumors with areas that, when viewed under the microscope, look like each of the 3 layers of a developing embryo: the endoderm (innermost layer), mesoderm (middle layer), and ectoderm (outer layer). This germ cell tumor has a benign form called mature teratoma and a cancerous form called immature teratoma.

The mature teratoma is by far the most common ovarian germ cell tumor and usually affects women of reproductive age (teens through forties). It is often called a dermoid cyst because its lining resembles skin. These tumors or cysts can contain different kinds of benign tissues including, bone, hair, and teeth. The patient is cured by surgically removing the cyst.

Immature teratomas occur in girls and young women, usually younger than 18. These are rare cancers that contain cells that look like those from embryonic or fetal tissues such as connective tissue, respiratory passages, and brain. Tumors that are not very immature (grade 1 immature teratoma) and have not spread beyond the ovary are cured by surgical removal of the ovary. When they have spread beyond the ovary and/or much of the tumor has a very immature appearance (grade 2 or 3 immature teratomas), chemotherapy is recommended in addition to surgery to remove the ovary.

Dysgerminoma

Although this type of cancer is rare, it is the most common ovarian cancer of germ cells. It usually affects women in their teens and twenties. Although dysgerminomas are considered malignant (cancerous), most do not grow or spread very rapidly. When they are limited to the ovary, more than 75% of patients are cured by surgically removing the ovary, without any further treatment. Even when the tumor has spread further (or if it comes back later), surgery and/or chemotherapy is effective in controlling or curing the disease in about 90% of patients.

Endodermal sinus tumor (yolk sac tumor) and choriocarcinoma

These very rare tumors typically affect girls and young women. They tend to grow and spread rapidly but are usually very sensitive to chemotherapy. Choriocarcinoma that starts in the placenta (during pregnancy) is more common than the kind that starts in the ovary. Placental choriocarcinomas usually respond even better to chemotherapy than ovarian choriocarcinomas.

Stromal tumors

About 5% to 7% of ovarian cancers are ovarian stromal cell tumors. Most of these are granulosa cell tumors. More than half of stromal tumors are found in women older than 50, but about 5% of stromal tumors occur in young girls. The most common symptom of these tumors is abnormal vaginal bleeding. This happens because many of these tumors produce female hormones (like estrogen). These hormones can cause vaginal bleeding (like a period) to start again after menopause, or can cause menstrual periods and breast development in young girls. Less often, stromal tumors make male hormones (like testosterone). If male hormones are produced, the tumors can disrupt normal periods and cause facial and body hair to grow. Another symptom of stromal tumors can be sudden, severe, abdominal pain. This occurs if the tumor starts to bleed. Types of malignant (cancerous) stromal tumors include granulosa cell tumors, granulosa-theca tumors, and Sertoli-Leydig cell tumors, which are usually considered low-grade cancers. Thecomas and fibromas are benign stromal tumors.

Ovarian cysts

An ovarian cyst is a collection of fluid inside an ovary. Most ovarian cysts occur as a normal part of ovulation (release of eggs) - these are called "functional" cysts. These cysts usually go away within a few months without any treatment. If you develop a cyst, your doctor may want to check it again after your next cycle (period) to see if it has gotten smaller. In a female who isn't ovulating (like a woman after menopause or girl who hasn't started her periods), an ovarian cyst is a little more concerning, and the doctor may want to do more tests. The doctor may also order other tests if the cyst is large or if it does not go away in a few months. Even though most of these cysts are benign, a small number of them could be cancer. Sometimes the only way to know for sure if the cyst is malignant is to take it out with surgery. Benign cysts can be observed (follow-up with physical exams and imaging tests), treated with medicines, or removed with surgery.