Posted on February 5th, 2009 by
By Jenny Maxon, RN
At present, research in breast cancer has been evaluating the use of magnetic resonance imaging (MRI) as a screening test. Although initial results have indicated that MRI appears to be more effective than mammography at detecting early breast cancers, the cost of MRI and its ability to distinguish between breast cancer and other medical conditions of the breast are limiting its widespread use as a routine screening test for all women. If in the future these issues are resolved, MRI may work its way toward replacing or augmenting mammography for the early detection of breast cancer in the general population.
For now MRI has been reserved for women considered at high risk of developing breast cancer, but its role in breast cancer prevention is just beginning.
MRI in High-risk Women
An MRI is different from a mammogram in that it does not utilize X-rays; rather, it uses properties of magnets to create pictures of the body on a screen. During an MRI scan, the patient essentially lies in a very strong magnet. Signals of varying magnetic fields that are much weaker than the main magnet are sent to the body and returned to an antenna. A computer then converts the signals into pictures, which are attached to a scanner.
An MRI can usually obtain pictures of any part of the body at nearly any desired angle; and MRIs tend to be more accurate than X-rays or computerized axial tomography (CT) scans at picturing soft-tissue parts of the body (i.e., parts of the body that are not bones). An MRI can produce pictures of various parts of the body in “slices,” like slices of a loaf of bread, which enables physicians to look inside of organs, tissues, or masses.
For women at higher-than-average risk of developing breast cancer within their lifetime, screening for the disease must include measures to maximize the detection of cancer in its earliest stages while balancing the rate of false-positives and medical costs. False-positives are readings that falsely indicate the presence of cancer in cases when cancer is actually not present. A high rate of false-positive readings can result in excessive and unnecessary biopsies, medical costs, time demands on the healthcare system and the patient, and anxiety for the patient and the family. Because the highest possible rates of early detection of breast cancer are imperative for high-risk patients, however, higher rates of false-positives in screening tests are acceptable among this group of patients than for the general public.
Studies have demonstrated that screening measures such as MRI used in addition to mammography, or as a single screening measure, improve detection rates of breast cancer for women considered to be at high risk of developing the disease, and they may ultimately save lives compared with mammography alone. And although false-positive rates tend to be higher with MRIs, this rate is considered acceptable when balanced with detection rates for these high-risk women.
According to the American Cancer Society, women with the following factors benefit from annual screening with MRI:
The American Cancer Society recommends against breast MRI screening in women with a lifetime risk of breast cancer of less than 15 percent. The optimal approach to the screening of women with an intermediate risk of breast cancer (lifetime risk between 15 and 20 percent) remains uncertain, and these women are encouraged to discuss the individual risks and benefits of screening options with their physicians. All women can help their physicians accurately determine their risk of breast cancer by collecting as much family health history as possible.
Data on MRI in High-risk Women
The following are highlights from a few recent clinical trials that evaluated the efficacy of MRI among women who were at high risk of developing breast cancer, some of which led to the American Cancer Society’s decision to establish MRI as an appropriate screening measure for this group of individuals.
Researchers from Italy conducted a clinical trial that included 278 women who were considered at high risk of developing breast cancer. These women had either a BRCA1 or BRCA2 mutation, a first-degree relative with a BRCA1 or BRCA2 mutation, or a strong family history of breast or ovarian cancer (defined as three or more first- or second-degree relatives with either a diagnosis of breast cancer at a young age if a female, a diagnosis of breast cancer at any age if a male, or ovarian cancer at any age). Women in the study underwent annual screening with a clinical breast exam, mammography, ultrasonography, and MRI. During the study’s time frame, 18 breast cancers were detected.
A second clinical trial was conducted by researchers from Canada and included 236 women with a BRCA1 or BRCA2 mutation. Women in this study underwent screening with mammography, ultrasound, MRI, and clinical breast exam between 1997 and 2003.
Researchers from Stanford University conducted a study to evaluate the cost-effectiveness of MRI on women with a BRCA1 or BRCA1 mutation. This study included the development of a statistical model to determine cost-effectiveness in screening measures for these women. The model estimated the health outcomes and the costs of different screening scenarios. These scenarios were: no screening, annual mammography from age 25 to age 69, and annual mammography from age 25 to age 69 plus annual MRI for specific age groups.
MRI in the General Population
The role of MRI for screening the general population for breast cancer is currently undergoing extensive evaluation. At present it appears that the general consensus among the medical community is that the cost and the false-positive rates of MRI are too high to warrant screening for breast cancer in individuals other than those who are considered at high-risk. If these prohibitive issues are somehow resolved in the future, however, results from studies may lead to the incorporation of MRI in routine screening for breast cancer.
Contralateral Breast Cancer
Women diagnosed and treated with breast cancer have up to a 10 percent chance of developing breast cancer in the contralateral (opposite) breast, even after clinical examination and mammography results demonstrate no indication of cancer. To address this issue, a recent clinical trial was conducted to evaluate the effectiveness of MRI screening of the contralateral breast among women newly diagnosed with breast cancer. This trial included 969 women with newly diagnosed breast cancer who had no abnormalities found on mammography or clinical examination of the contralateral breast. Patients then underwent screening with MRI.
Researchers from the University of Pennsylvania also reported a high rate of contralateral breast cancer among women diagnosed with breast cancer. In this study 1,801 women with early breast cancer had been treated with breast-conserving therapy between 1977 and 2000.
In yet another study, researchers from Sweden reported a 27 percent risk of developing contralateral breast cancer among women with hereditary breast cancer not due to a BRCA1 or BRCA2 mutation. This risk also persisted for 20 years.
Results from these three studies indicate the potential use of MRI in screening for contralateral breast cancer among women already diagnosed with breast cancer. Again, future studies evaluating this issue will provide guidance for optimal screening for contralateral breast cancer and the potential use of MRI.
MRI in Ductal Carcinoma in Situ
Research has also suggested that MRI provides effective screening for the earliest form of breast cancer: ductal carcinoma in situ (DCIS). A recent study included nearly 6,000 women who were screened with both MRI and mammography; a total of 167 cases of DCIS were diagnosed among these patients.
Screening for breast cancer with mammography has significantly improved survival rates among women affected by breast cancer. Improving on this, MRI has demonstrated additional survival benefit, particularly when used for screening high-risk women and for detection of cancer in the contralateral breast.
Results from further clinical studies will guide the use of MRI, or other novel screening measures, into the clinical setting of breast cancer screening. If the main issues of medical costs and false-positive rates are surmounted, MRI may play additional roles in breast cancer screening. For now women should speak with their physicians regarding their family history of breast cancer to best determine their optimal screening regimen, the possibility of participating in clinical trials evaluating newer screening measures, or addressing issues with MRI screening for this disease.
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