Currently, mammography is the only exam approved by the U.S. Food and Drug Administration (FDA) to screen for breast cancer in women with no signs of breast cancer. However, ultrasound (also called sonography) may also be useful in detecting breast cancer, according to a new study. The study found that in women with dense breast tissue, ultrasound found a significant number of cancers in patients whose mammograms appeared normal. While the researchers are not recommending that ultrasound in any way replace mammography, they do say that ultrasound appears to be a helpful screening tool for these women when performed in conjunction with mammography.
Mammography is a special x-ray exam of the breasts. The goal of screening mammography is to detect breast cancer when it is still too small to be felt by a physician or the patient. The National Cancer Institute recommends that women begin receiving screening mammograms every one to two years at 40 years of age and every year once they reach 50 years of age. Mammography detects approximately 85% of all breast cancers.
While mammography can found most breast cancers, the exam tends to be less successful in women who have dense breast tissue. Dense, or thick breast tissue shows up as a white region on the mammogram film. However, a breast cancer tumor also appears white on the mammogram. Therefore, dense breast tissue can sometimes eclipse the breast cancer.
In a study presented at a recent meeting of the American Medical Association, Thomas Kolb, MD of Columbia-Presbyterian Medical Center in New York said that he and his colleagues examined 13,547 women with dense breast tissue. Previous mammograms and physician-performed clinical breast exams did not reveal any suspicious breast abnormalities. However, after performing ultrasound, 246 cancers were detected among the women.
Dr. Kolb says that breast cancer tends to be easier to detect in dense breasts with ultrasound due to its high contrast resolution. Ultrasound enables physicians to clearly distinguish between dense breast tissue and cancer. However, Dr. Kolb also noted that ultrasound tends to miss breast cancers a high percentage of the time; thus, it is not an effective screening tool on its own. It may be best used among women with dense breasts in addition to mammography and physical breast exam. Women with normal, non-dense breast tissue are likely to benefit less from screening ultrasound, and most insurance companies do not routinely cover ultrasound as a screening exam.
Ultrasound has several other limitations as a screening tool. A main disadvantage to ultrasound is that it is typically unable to detect calcifications—tiny calcium deposits that are often associated with breast cancer. Mammography, on the other hand, is highly effective at detecting these calcifications.
Ultrasound may also have a difficult time imaging a breast abnormality that can be felt due to:
- The deep location of the abnormality within the breast
- Operator and equipment factors
- The ultrasound image contrast between the abnormality and the surrounding breast tissue
Other diagnostic exams, such as magnetic resonance imaging (MRI), have shown some promise in detecting breast cancer. However, breast MRI tends to be expensive and not widely available. It also has far less accuracy than mammography at detecting cancer in women with no signs of the disease. Therefore, overall, mammography remains the most accurate method of screening for breast cancer.
