An ovarian tumor is a growth of abnormal cells that may be either noncancerous (benign) or cancerous (malignant). Although benign tumors are made up of abnormal cells, these cells don't spread to other body tissues (metastasize). Malignant cells metastasize and may spread directly into other tissues, or may detach from the original tumor site and spread through your body by way of blood vessels or lymph nodes.

Although the exact cause of ovarian cancer is unknown, three basic types of tumors exist and are designated by where they form in the ovary. They include:

• Epithelial tumors. About 90 percent of ovarian cancers develop in the epithelium, the thin layer of tissue that covers the ovaries. This is the most common form of ovarian cancer and generally occurs in postmenopausal women.

• Germ cell tumors. These tumors occur in the egg-producing cells of the ovary and generally occur in younger women.

• Stromal tumors. These tumors develop in the estrogen- and progesterone-producing tissue that holds the ovary together.

Several factors may increase a woman's risk of ovarian cancer. Having one or more of these risk factors doesn't mean that you're sure to develop ovarian cancer, but your risk may be higher than that of the average woman. These risk factors include:

• Family history. This is the most important risk factor for ovarian cancer. A family history of ovarian cancer in a first-degree relative — mother, daughter or sister — increases your risk of developing the disease. The likelihood is greater if two or more first-degree relatives have had ovarian cancer. A family history of breast or colorectal cancer also is associated with an increased risk of ovarian cancer.

• Age. Ovarian cancer generally develops after menopause, and women older than 60 are at highest risk. Although most cases of ovarian cancer are diagnosed in older women, the disease can also occur in younger women.

• Childbearing status. Women who have had at least one pregnancy appear to have a lower risk of developing ovarian cancer. Similarly, the use of oral contraceptives appears to offer some protection against ovarian cancer.

• Infertility. If you've had trouble conceiving or had your first child late in life, you may be at increased risk.

• Endometriosis
• Infertility, female
• Infertility, male

• menopause

Some women who develop ovarian cysts have no symptoms, but have cysts that are found by their physician during a pelvic examination. Cyst formation is a normal part of ovulation in premenopausal women. However, cysts that don't go away or that occur after menopause need to be evaluated. Doctors don't know if these benign ovarian cysts develop into ovarian cancer, but it's recommended that they be removed. Types of ovarian cysts include:

• Dermoid cysts. These cysts are actually benign tumors called teratomas. They may contain tissue such as hair, skin or teeth because they form from cells that produce human eggs. They're seldom cancerous, but can become large and cause painful twisting of the ovary and fallopian tube.

• Endometriomas. If you have endometriosis, a condition in which uterine cells grow outside your uterus, some endometrial tissue may attach to the ovary and form a cyst.

• Cystadenomas. These cysts develop from ovarian tissue and may be filled with a watery liquid or a mucous material. They can become large and cause twisting of the ovary and fallopian tube.

No test can determine with perfect accuracy whether an ovarian cancer growth or cyst is benign or malignant. However, the following characteristics can help your doctor in assessing an ovarian growth:

• Size of the cyst. A small percentage of growths smaller than about 2 inches in diameter are cancerous. The likelihood of cancer increases with the size of the growth. Your risk of ovarian cancer can be more than 60 percent when a growth is larger than 4 inches.

• Your age. If you're 50 or older, the likelihood that your cyst is malignant is 25 percent. Once you reach your 80s, the chance increases significantly.

• The postmenopausal years. Only about 10 percent of postmenopausal ovarian cysts are normal monthly (functional) cysts. The remainder are tumors that can be either benign or malignant. Doctors don't know why ovarian cysts form after menopause.

• Endometriosis

• menopause

Although the majority of cases of ovarian cancer occur in women who don't have a strong family history of the disease, a small number of ovarian cancer cases are linked to a genetic predisposition for the disease.

Other factors may play a role in a woman's increased risk of ovarian cancer. More research is needed to confirm these findings. These factors include:

• Fertility drugs. Researchers are exploring a possible role of fertility drugs — which are used to cause ovulation — in increasing the risk of ovarian cancer.

• Hormone replacement therapy (HRT). Women who use HRT after menopause may be at increased risk of developing ovarian cancer. HRT may have other negative effects as well. Taking HRT as a combination therapy — estrogen plus progestin — can result in serious side effects and health risks. If you're considering HRT, work with your doctor to evaluate the options and decide what's best for you.