Genetics and Ovarian Cancer
Q. Is ovarian cancer inherited?
A. The majority of
ovarian cancers are caused by unknown factors. About 5-10% of ovarian cancers are caused by inherited factors (e.g., abnormalities in genes, known as mutations, which may be inherited from either parent). In this situation, a woman may be born with (inherits) a mutation in a gene that predisposes her to the development of ovarian cancer. At least two patterns of hereditary ovarian cancer have been described. In the first, a patient with ovarian cancer may have other family members with
breast cancer, ovarian cancer, or even both tumors in the same individual. This is known as the breast/ovarian cancer syndrome. In the second, an ovarian cancer patient may have family members with a variety of other tumors (see below), including
colorectal cancer and
endometrial (uterine) cancer. This is sometimes referred to as the Lynch syndrome II.
Q. What genes are involved?
A. Most hereditary ovarian cancers occur in families with the breast/ovarian cancer syndrome and are associated with inherited mutations in one of two genes known as BRCA1 and BRCA2. BRCA1 mutations account for the majority of cases of inherited ovarian cancer (50%-70%), while BRCA2 mutations are less common (15-25%). When a parent has a mutation in a gene such as BRCA1 or BRCA2, there is a 50% chance of passing on the mutation to each of his or her children.
Families with the Lynch syndrome II usually include several individuals who develop bowel (colon or rectal) cancer, often before age 50. These bowel tumors are usually not associated with polyps and are therefore sometimes called "hereditary non-polyposis colon cancer" (HNPCC). Other tumors which may affect members of these families include endometrial, ovarian, stomach, small bowel, bile duct, and urinary tract cancers. Lynch syndrome II is caused by a mutation in one of several different genes known as mismatch repair genes. The two genes responsible for the majority of mutations found are known as MSH2 and MLH1. Less commonly mutations can be found in the PMS1, PMS2 and MSH6 genes. In at least one third of families with the Lynch syndrome II, no identifiable mutation is found.
Q. How do I suspect that breast or ovarian cancer in my family might be inherited?
A. Some situations increase the likelihood (but do not necessarily mean) that an inherited form of cancer may exist in a family:
- Breast and/or ovarian cancer occurring in at least three close relatives.
- Breast and/or ovarian cancer occurring at an early age (before
- Breast and ovarian cancer occurring in the same family member.
- Men in the family with breast cancer (suggests BRCA2 mutation).
- Family members with bowel cancer at an early age (before 50), endometrial cancer, or other Lynch syndrome associated cancers (see above).
Q. What is genetic testing?
A. Scientists are now able to look for mutations in genes with a blood test. This genetic test can sometimes determine if an individual has an inherited form of ovarian cancer. If a mutation is found, other family members can learn if they have inherited the same mutation and therefore have an increased risk for cancer. It is preferable to begin the process of genetic testing in a patient already affected with cancer, since a specific mutation found in that individual would make the search for the same mutation in other family members much easier. Several types of mutations in BRCA1 and BRCA2 are more common in certain ethnic groups. Your physician will be able to provide you with more details as appropriate.
Q. What are my options if I have a BRCA1 or BRCA2 mutation?
A. A woman with a mutation in BRCA1 or BRCA2 has an increased chance of developing breast cancer and/or ovarian cancer. There are several strategies one can use to try to prevent cancer from occurring, or to increase the chance of detecting it early. While no method for prevention or early detection has yet been proven to be completely effective, options include:
Increased surveillance (cancer screening). Breast cancer may be detected with surveillance measures such as breast self-exams, mammograms, MRI's, and breast exams performed by your doctor. Likewise, pelvic ultrasounds and a blood test called CA-125 are sometimes used in an attempt to detect ovarian cancer at an early stage. Whether these surveillance measures can result in early cancer detection and lead to improved survival in patients with BRCA1 or BRCA2 mutations is unknown. Surveillance usually starts between the ages of 25 to 35, or 10 years prior to the youngest known affected relative.
Prophylactic (preventive) surgery. This approach involves removing the breasts and/or ovaries before cancer can develop. It is important to remember, however, that it is not possible to remove all of the breast tissue, and a small number of women can still develop breast cancer even after the surgery. Likewise, a type of ovarian cancer starting inside the abdomen can occasionally develop, even in patients whose ovaries are prophylactically removed. The impact of these procedures on survival remains uncertain, although consideration of prophylactic surgery in selected women is reasonable and the results of published studies show a significantly reduced risk of developing these cancers. The pros and cons of this approach need to be carefully discussed between you and your physician.
Chemoprevention. A recently published national trial (the Breast Cancer Prevention Trial) demonstrated that women who took a medication called tamoxifen for five years reduced their risk of developing breast cancer by 50% compared to women who took a placebo. The second national breast cancer prevention trial, known as the STAR study, will compare tamoxifen to a newer tamoxifen-like drug called raloxifene, in order to determine which drug is superior in preventing breast cancer. It is not yet known whether these medications reduce the risk of developing breast cancer in BRCA1 and BRCA2 mutation carriers. Other research has shown that women who have used birth control pills have a lower incidence of developing ovarian cancer (a recent study suggests that this may also be the case for women who carry a BRCA1 mutation).
Q. What are my options if I have a Lynch Syndrome associated mutation?
A. Individuals with a Lynch Syndrome mutation are at especially high risk for developing colorectal cancer, although the risk for other tumors such as those involving the endometrium (uterus), ovaries, and stomach is increased as well. A procedure known as
colonoscopy should be frequently performed to detect colon cancer and/or to remove precancerous lesions in patients with the Lynch syndrome. Screening tests for cancers at other sites are of uncertain value and are beyond the scope of this section. Your physician will be able to provide you with more details as appropriate.
Above content provided by Beth Israel Deaconess Medical Center. For advice about your medical care, consult your doctor.
Posted July 2010