For decades, the mammogram has been the sole recommended, regular imaging procedure for detecting breast cancer. Women over the age of 40, regardless of risk level, are advised to get mammograms -- which use X-rays to look inside the breast -- at least every other year. Women at high risk should start earlier and get tested more often. This has been the standard of care. But in March 2007, two different sources released information recommending that MRI, a magnetic imaging technique, be included in the standard testing procedures for certain women.
The most far-reaching news is a set of guidelines published by the American Cancer Society, which states that women who are in the high-risk group for breast cancer should add MRIs to their regular, yearly testing regimen. MRIs do not replace annual mammograms; they are a supplemental tool that can detect certain tumors that mammograms miss. But breast MRIs have downsides that makes them less ideal for any woman who is not in the high-risk group.
A breast MRI (magnetic resonance imaging), uses magnetism and radio waves to create multiple images of the breast from every possible angle. An extremely high-power magnet creates a magnetic field inside the MRI machine, where the patients is lying for 30 to 60 minutes, and switches the orientation of the field while the machine pulses radio waves into the breast tissue. The radio waves bounce back, or echo, off the various levels of breast tissue, and a magnetized coil surrounding each breast measures the intensity of the echoes. By altering the orientation of the magnetic field throughout the exam, the machine creates views of the breast on every axis -- side to side, front to back, and top to bottom. (See How MRI Works to learn more about the process.)
There are big benefits to MRI. First, there's no radiation involved like there is in a mammogram. And it doesn't require the breast to be flattened, which means it's less uncomfortable than a mammogram. And the big plus is that an MRI can pick up way more abnormalities than a mammogram can. It's unhindered by especially dense breast tissue, which most young women have, and by breast implants, both of which can obscure a tumor on a mammogram. It also images the breast on more planes than a mammogram does, creating a much more detailed view that reveals even subtle differences in breast density, which can be indicators of cancer.
But the biggest plus is also the biggest negative of the breast MRI. It picks up almost everything. If anything looks the slightest bit weird, an MRI is going to reveal it. But there are many, many weird-looking things that show up on breast images that have nothing to do with cancer. Some estimates put MRI false-positives at one in 10, meaning women end up getting a lot of unnecessary cancer terror and invasive biopsies. This is why MRIs are not recommended for women in the average-risk group. Unless there's a pretty good chance you're going to get breast cancer, it doesn't make sense to go through a testing procedure that produces a false positive 10 percent of the time.
And while MRI doesn't use radiation, it does require the injection of a dye to produce greater contrast on the images, and it has trouble picking out certain types of calcifications that can indicate the presence of cancer. Mammograms can see those calcifications. Also, people who are claustrophobic can have problems being in an MRI machine for up to an hour, and the procedure costs about 10 times more than a mammogram. Some insurance plans cover it, but some don't. A woman in the high-risk group would have to spend at least $1,000 a year on a breast MRI if her insurance won't pay for it. Which brings us to another problem: figuring out who's in the high-risk group.
High Breast-cancer Risk
No one has a definite answer to how breast-cancer risk should be determined. "High risk" is typically defined as a 20 percent chance of getting breast cancer, but risk factors are pretty qualitative. Most guidelines state that high-risk women are those who are over 30 and have:
- more than one close relative (mother, sister, daughter) who has had breast cancer
- a genetic mutation linked to breast cancer (a mutated BRCA1, BRCA2, TP53 or PTEN gene)
- a close relative with a genetic mutation linked to breast cancer
- radiation treatment to the chest area after the age of 10 and before the age of 30
Even with these guidelines, the only way to know if you're really in the high-risk group is to discuss it with your doctor. Some woman who meet one or more of these criteria are actually in the average-risk group and should not be getting an MRI every year.
The second source promoting the regular use of MRI in breast-cancer testing is a new study published in the New England Journal of Medicine, and it really only applies to women who are diagnosed with breast cancer. This new research suggests that women who have been diagnosed with breast cancer in one breast should absolutely get an MRI of the other breast, even if the mammogram is clear, before beginning cancer treatment.
The study involved 969 women who had been diagnosed with a malignant tumor in one breast and had a mammogram of the other breast that revealed no cancer. Each of the women then received an MRI of the non-cancerous breast. In 30 cases, the MRI revealed that there was in fact cancer in the other breast. Without the MRI, those 30 women -- 3 percent of the subjects in the study -- would have begun treatment for cancer in one breast only to find out later it was also in the other breast. The second cancer would have been detected at a later stage, making it more serious, and the woman might have had to go through an entire second round of treatment involving surgery, chemotherapy and/or radiation. In cancer terms, a 3 percent chance of a false negative is unacceptable if it can be avoided with a non-invasive procedure that takes an hour.
With the back-to-back release of two credible recommendations for MRI as a regular breast-cancer detection method, it's likely that insurance companies that don't cover the procedure will start doing so very soon.
For more information on breast cancer, MRI and related topics, check out the links on the next page.
Related HowStuffWorks Articles
More Great Links
- "Breast MRIs urged for high-risk women." CNN.com. Mar. 28, 2007. http://www.cnn.com/2007/HEALTH/conditions/03/27/ breast.mri.ap/index.html
- Grady, Denise. "Call to Increase M.R.I. Use for Breast Exam." The New York Times. Mar. 28, 2007. http://www.nytimes.com/2007/03/28/health/28mri.html? ex=1175745600&en=811b28ffc55cd3e9&ei=5070
- "Magnetic Resonance Breast Imaging." Imaginis. http://www.imaginis.com/breasthealth/mri.asp
- "MRI Detects Cancers In The Opposite Breast Of Women Newly Diagnosed With Breast Cancer." ScienceDaily. March 28, 2007. http://www.sciencedaily.com/releases/2007/03/070328073156.htm
- "What is Breast MRI?" UCSF Department of Radiology. http://www.mrsc.ucsf.edu/breast/what_is_breast_mri.html