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Wednesday, March 28, 2007

Answers to questions about scans for breast cancer

The American Cancer Society yesterday recommended for the first time that certain women get annual magnetic resonance imaging (MRI) scans for breast cancer, even though they have no signs of the disease.

The guidelines are intended for women at unusually high risk of cancer, but it left many women wondering whether they need one of these high-tech scans. Below, Globe reporter Scott Allen answers some basic questions about screening for breast cancer, the second deadliest cancer for women.

Q. What is an MRI and what makes it preferable to a mammogram?
A. Magnetic resonance imaging, or MRI, uses magnetic fields to generate cross-sectional views of soft tissue, creating images that look like detailed "slices" through the breast. The patient typically receives an intravenous injection of a dye to make potential tumors stand out more clearly, then she must hold still for 30 to 45 minutes while the MRI generates images of the breast. The procedure doesn't hurt, though the machine makes rhythmic thumping noises and some people feel claustrophobic inside the MRI tube.

Half-a-dozen major studies of women at high risk of breast cancer have shown that MRI identifies at least twice as many potential tumors as a conventional mammogram, which produces a two-dimensional X-ray or digital picture. The best quality MRI images are produced in MRIs designed specifically for breasts, where the woman lies face down on the bed, placing her breasts in a cut-out area.


Q. What are the drawbacks of an MRI scan?
A. MRI's generate far more cancer "false alarms" than mammograms because many of the suspected tumors identified by MRI turn out to be healthy tissue. Doctors are twice as likely to request a tissue sample based on an MRI image compared to a mammogram, requiring a minor surgical procedure called a biopsy. But 60 to 80 percent of the time, the biopsied tissue is not cancerous.

In addition, MRI costs up to 10 times more than a mammogram and not all insurance policies cover the high-tech scans for women who show no signs of cancer. However, the level of insurance coverage is likely to increase now that the American Cancer Society has recommended routine MRI screening for high-risk women.


Q. Who should get an annual MRI scan?
A. Women who face a very high risk of cancer -- defined as a lifetime breast cancer risk of at least 20 percent -- should get annual MRIs, according to the Cancer Society guidelines. That includes women who know they carry one of the so-called "breast cancer genes" -- mutations of BRCA1 and BRCA2 -- as well as close relatives who have not yet been tested. In addition, women with a strong family history of breast or ovarian cancer should get an MRI if they score above a 20 percent cancer risk using a statistical model called BRCAPRO.

The Cancer Society also calls for annual MRIs for women who suffer from several rare disorders as well as women who were treated with radiation to the chest -- usually for Hodgkin's Disease -- between the ages of 10 and 30. More details about the guidelines can be found on the Cancer Society's web site.

Finally, women who have been recently diagnosed with breast cancer should immediately get an MRI scan of the other breast to be sure there are no other tumors, according to a separate study in the New England Journal of Medicine this week.


Q. How can I estimate my lifetime cancer risk?
A. Unfortunately, calculating the risk of cancer is not easy -- and a woman should not automatically conclude that she faces a heightened risk of cancer even if her mother suffered from the disease. Doctors need a complete family medical history and a computer model to calculate lifetime risk, taking into consideration the number of relatives who suffered ovarian or breast cancer and the age at which they were diagnosed.

And the results can be surprising:

For example, a 35-year-old woman whose mother had breast cancer at 51 and whose maternal aunt was diagnosed with the disease at 60 faces only a 13 percent lifetime risk of breast cancer, which is not high considering that 12.7 percent of all women will develop breast cancer at some point in their lives.

By comparison, a 35-year-old woman whose paternal aunt developed both breast and ovarian cancer by age 49 and whose paternal grandmother had breast cancer at 35 faces a lifetime cancer risk of 23 percent. Based on the Cancer Society guidelines, she should get an annual MRI in addition to a mammogram.

The National Cancer Institute has developed a risk calculator . However, Cancer Society officials say women should contact their doctors to discuss the results.


Q. If I get an MRI, can I skip my mammogram?
A. No. Even though MRIs detect more tumors, radiologists regard mammograms as valuable tools that can spot some types of breast cancer better than MRIs. A British study in 2005 found that X-ray mammograms alone spotted 40 percent of the known tumors in high-risk women compared to 77 percent detected by MRI. When the two methods were combined, the researchers picked up 92 percent of the tumors.


Q. What about women whose lifetime cancer risk is less than 20 percent?
A. The Cancer Society panel concluded there isn't enough evidence to recommend MRIs for women whose cancer risk is only somewhat elevated, estimated at 15 to 20 percent lifetime risk. That would include women whose breast tissue is especially dense, making tumors harder to see on M-ray mammograms, as well as women who have experienced some forms of breast cancer, such as ductal carcinoma in situ, which is non-invasive and highly treatable. However, Cancer Society officials say that doctors may still want an MRI for some women in this group based on individual medical issues.

The Cancer Society urges all women to get annual mammograms from the time they are 40 and to perform regular self-exams because breast cancer is easiest to cure when it's detected early.

SOURCES: American Cancer Society, National Cancer Institute, New England Journal of Medicine.


Posted by Karen Weintraub at 06:29 PM
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