Advances in breast cancer screening: Good, better, breast
Reports on advances in breast cancer screening appear regularly in medical journals and even in the news, driven by the ongoing quest for earlier and more definitive breast cancer detection. After all, the earlier breast cancer is detected, the better the chances of successful treatment.
For nearly four decades now, mammography has been the gold standard method for detecting early breast cancer. On average, screening mammograms correctly identify 80 percent to 85 percent of women who have cancer and about 90 percent of women who don’t.
More recently, digital mammography has come into use, resulting in x-ray images that can be viewed and enhanced on computer screens. Additional imaging methods — such as magnetic resonance imaging (MRI) plus ultrasound when needed, and molecular breast imaging (MBI) —are also being used or studied for use in detecting and diagnosing breast cancer.
Tried and Often True
For women 40 and older, annual mammograms should be familiar. The American Cancer Society has long recommended annual mammograms for this age group. The standard mammogram involves producing an image on film using low-dose x-ray. However, conventional mammograms tend to be more useful for postmenopausal women than for premenopausal women. The difference is due to breast changes that occur with age. Younger women are more likely to have dense breast tissue, which can make abnormalities in the breast more difficult to pick up on a conventional mammogram. Mammogram sensitivity in women younger than 50 can be as low as 50 percent.
In addition to the challenges of dense breast tissue, there are other reasons some breast cancers are missed by mammography, including:
• Some breast cancers can look like normal breast structures on a mammogram or be obscured by normal breast tissue.
• It’s possible for some breast cancers to be excluded from the field of view on mammography.
Digital Mammography
In digital mammography, which was approved for diagnostic use in 2000, images are stored in a computer instead of on film. The technique may provide an edge in some cases.
A large clinical trial compared the accuracy of conventional and digital mammography on nearly 50,000 women. Results, published in 2005, showed that the accuracy of the two kinds of mammography was similar, but digital was more accurate in premenopausal women, women younger than 50, and women with dense breasts.
Another study published last year found that breast cancer rates nearly doubled — from 4.1-4.5 per 1,000 women to 7.9 per 1,000 — at a diagnostic center in California after the center switched to digital mammography. One study also found that the average radiation dose per view was 22 percent lower for digital mammography than for analog.
But digital mammography is not available everywhere. (In the Philippines, it is available at a few of our top medical centers). And experts agree that it’s more important simply to get a mammogram than to wait to get a digital one, if none is easily available in your area.
Seeing With Sound
If a mass or suspicious area is detected on a mammogram, ultrasound may be used as a follow-up test. Ultrasound uses high-frequency sound waves to create images of breast tissue. It can determine whether a suspicious area is a harmless cyst or a solid mass that could be cancerous.
Breast density doesn’t interfere with ultrasound results, hence ultrasound may be used along with mammography in evaluating women with dense breasts. However, ultrasound can’t reliably detect small calcium deposits, which may be an early sign of breast cancer. For that reason, it’s not recommended as a routine screening tool in place of mammography. Researchers are investigating whether mammography, combined with ultrasound screening, is more effective at detecting cancers than mammography alone.
A Place for Magnets
Magnetic resonance imaging (MRI) combines computer power with powerful magnets (see diagram). Breast imaging with MRI takes about 45 to 60 minutes. It involves no radiation and produces thousands of images of each breast. Usually, a contrast agent is injected into a vein to help enhance breast tissue areas where there may be abnormal blood vessels, which may indicate the presence of cancer.
MRI may be used to further assess an abnormal area seen on a mammogram. In women diagnosed with breast cancer, it may be used to help determine the extent of a tumor and to screen for possible second cancers in either breast. In addition, MRI may be used to monitor treatment of known breast cancer — for instance, when chemotherapy is being used prior to surgery to help shrink larger cancers.
MRI currently isn’t recommended for routine breast screening. Not only is it costly and not widely available, compared with traditional mammography, it also may have a higher rate of false positives — meaning it indicates cancer might be present when it’s not. However, MRI may be of particular use in monitoring women who are considered to be at higher risk of developing breast cancer.
The American Cancer Society (ACS) recommends that women at high risk of breast cancer have both a mammogram and an MRI. Women considered to be at high risk include those who have:
• A known gene mutation to the BRCA 1 or BRCA 2 genes.
• An immediate family member — meaning your mother, father, sibling or child — has the BRCA 1 or BRCA 2 gene mutation, but you have yet to be tested yourself.
• A lifetime risk of breast cancer that’s 20 percent or greater, based mainly on family history.
• Had radiation therapy to the chest before age 30.
If you’re at moderately increased risk, the ACS recommends talking with your doctor to decide whether to have an MRI with your annual mammogram. Moderate increased risk includes women with a lifetime breast cancer risk of 15 percent to 20 percent, based mainly on family history, or extremely dense breast tissue as viewed on mammogram.
For most high-risk women, screening usually should begin at age 30 or at a time determined jointly with your doctor. Otherwise, screening should begin at age 40 — or 10 years before the age at which a close relative developed breast cancer, if that relative developed breast cancer at an age younger than 40.
Molecular Breast Imaging
Researchers at Mayo Clinic are studying a new type of imaging technique to detect breast cancer. It’s called molecular breast imaging (MBI). The technique involves the use of a short-lived radioactive agent, which is injected into a vein to highlight any abnormalities that may be in the breast tissue. Tumors generally absorb more of the radioactive agent than does healthy breast tissue. A specialized camera is used to observe areas in the breast where the injected material accumulates, essentially illuminating any abnormalities in the breast. Unlike some other imaging techniques, very dense breast tissue doesn’t interfere with MBI results.
In one study reported at last year’s meeting of the American Association of Physicists in Medicine, MBI found 10 out 13 tumors while mammograms found only three out of 13 tumors. These results suggest that MBI could become an important screening tool for women who have dense breast tissue and increased breast cancer risk. Although MBI isn’t in clinical use yet, the cost would likely fall between that of digital mammography and MRI. The downside, MBI uses eight to 10 times more the radiation used in mammograms. Researchers are testing lower doses.
A Final Word
Although MRI and other imaging techniques are generally considered less uncomfortable, mammograms today remain the mainstay in breast cancer screening. That may change, but for now, mammograms continue to be the best technique available to screen women for breast cancers.
Scientists around the world are exploring a range of technologies to discover new screening tests for breast cancer with better precision, and they are learning more and more every day. Some day we hope that we will have one that will be cheap, painless, and accurate — which will diagnose breast cancer at its earliest stage and provide a cure for those who will get them.
