What are the risk factors for ovarian cancer?

"How can that be?" Mrs. G. thought as she sat in her gynecologist's office, stunned by the news that her pelvic ultrasound suggested ovarian cancer.  "I don't have cancer in my family!"

In the United States, the most challenging gynecologic cancers are ovarian cancer and the closely related malignancies that arise in the fallopian tube and the lining of the abdominal cavity.  Because ovarian cancer, often together with breast cancer, does run in families, many women without a significant family history -- women like Mrs. G -- feel they are not at risk. However, about 85% of ovarian cancers have no hereditary link.

Ovarian cancers affect about 23,000 American women every year, and cause 14,000 deaths.  The average American woman has about a 1 in 75 chance of developing ovarian cancer, and a 1 in 100 chance of succumbing to it.

Although there are several kinds of ovarian cancer, by far the most common type develops from the cells that cover the surface of the ovary or line the fallopian tubes, the so-called epithelial cancers of the ovary.  Risk factors for these cancers have been intensively studied for many years. They include:

For about 15% of women with ovarian cancer, inheriting a gene abnormality that predisposes them to cancer -- most often the BRCA 1, BRCA 2, and Lynch family genes -- causes tumor growth.

An abnormality in one of these genes can be inherited from either parent. If a parent carries the genetic defect, the chance of passing it on to a child is 50%.  While not everyone who inherits such a gene will develop cancer, the risk of ovarian, breast, and other cancers is quite high for those who carry an abnormal BRCA gene, as is the risk for ovarian, uterine, GI and certain other cancers for those with an abnormal Lynch gene.

Men who carry these abnormal genes are at increased risk of certain cancers, including prostate cancer.

Fortunately, genetic testing is widely available and usually covered by insurance. Federal law prohibits discrimination from health insurers and employers based on the results of genetic testing.

Current recommendations are that all women diagnosed with ovarian cancer should undergo genetic counseling and testing, as should any woman with a worrisome family history of cancer.  Women who test positive have numerous options to reduce their risk of cancer, and information from the test may be of great help to family members.  As I tell my patients, "Knowledge is power, and ignorance is not bliss."

The average age at diagnosis of ovarian cancer in the U.S. is 63.  The risk for developing ovarian cancer increases with age, so by age 70, women have approximately double their risk at age 50.

Women with an inherited genetic defect who develop cancer are often diagnosed at a younger age.

The risk of ovarian cancer is reduced by about half in women who have used an oral contraceptive for several or more years, probably because oral contraceptives inhibit the production and release of eggs from the ovaries.  For similar reasons, pregnancy and breastfeeding lower the risk of ovarian cancer.  Tubal ligation and hysterectomy, even when the ovaries are not removed, also somewhat reduce the risk.

There are several reproductive factors that may increase the chance of developing ovarian cancer, including infertility, endometriosis, and perhaps the use of menopausal hormone replacement therapy.  Medications used to stimulate ovulation in the treatment of infertility are not thought to be an independent risk factor for ovarian cancer.

Cigarette smoking, a deadly habit for other reasons, may also increase the risk of some types of ovarian cancer.  The relationship between genital exposure to talcum powder and ovarian cancer risk is controversial, but some studies have reported an elevated risk.  Obesity may slightly increase the risk of ovarian cancer, as may a diet high in animal fat.  Alcohol use is not known to be a risk factor.

Women concerned about their risk based on family history should ask to be referred for genetic counseling and testing.  Women who have an ovarian tumor that might be malignant, based on radiologic scans or blood tests, should ask to be referred to a gynecologic oncologist, a specialist in the diagnosis and treatment of gynecologic cancers.

Stephen C. Rubin, M.D. is the Chief of the Division of Gynecologic Oncology at the Fox Chase Cancer Center.

Read more Diagnosis: Cancer here »