Mammography is accepted as a highly accurate way to detect breast cancer, but it doesn't pick up every tumor. A new study suggests that adding an ultrasound may increase the chance of detection in women at high risk of developing the disease.
Dr. Wendie Berg, the study's lead researcher, is a radiologist at Johns Hopkins University. She was interested in finding out whether ultrasound could pick up tumors that mammography could not, something earlier studies had suggested.
Berg and her team recruited more than 2,800 women at 21 different imaging centers across the United States for the study, which was conducted from April 2004 to February 2006. All participants were at least 25 and had an elevated risk of the disease.
The researchers found that mammography alone had a cancer detection rate of 7.6 women per 1,000 women screened. Adding an ultrasound boosted the rate to 11.8 women per 1,000 women screened – an increase of 28 percent. The results of the study were published in the May 14 issue of The Journal of the American Medical Association.
The women who took part had dense breast tissue, which can make it more difficult for a mammogram machine to detect cancer. Berg says the tissue shows up as white on a mammogram — the same color as cancer.
"Ultrasound is a completely different way of looking at the breast tissue that is not at all limited by how dense the breast tissue is," Berg says. "It's just using sound waves to penetrate the breast tissue, and we see cancers because they're darker, usually, than the tissue around them."
"The types of cancer that we see with ultrasound are still small but they are invasive cancers — they're the type that spread when they are not detected," she explains. "And in this study we found that the vast majority of cancers we found with ultrasound had not yet spread to lymph nodes. And that's important. Those are the types of cancers that we need to be finding."
Berg says these are tumors that could eventually become lumps large enough to be detected during a routine breast exam — cancers that might have also spread to lymph nodes.
About 182,460 women are expected to be diagnosed with invasive breast cancer in the U.S. this year, according to the American Cancer Society.
Risk of False Positives
Berg cautions that while the results of the study are encouraging, there are drawbacks to using ultrasound. The ultrasound was four times more likely than the mammogram to produce a false positive, which could lead to unneeded medical procedures.
"That's a fairly substantial risk of an unnecessary biopsy," she says. "Now for some women, they would still want to have the test, because it certainly has a chance of finding cancer when it's still early and treatable. ... But for other women that's too great a risk of a false positive, and they don't want to take that chance."
Biopsies are a surgical procedure requiring an anesthetic. The risk of an unnecessary biopsies means ultrasound should not be done routinely for all women, says Dr. Lawrence Bassett, director of the UCLA Iris Cantor Center for Breast Imaging.
Bassett says ultrasound should be done for women at high risk for breast cancer — those who have dense breast tissue or who have a close relative who was diagnosed with breast cancer before the age of 50.
And for women who carry an even higher risk — those whose previous biopsies have shown abnormalities or those who carry the breast cancer gene or have a close relative that does — then Bassett says an MRI is recommended. An MRI, which stands for magnetic resonance imaging, is far more sensitive — and costly --than an ultrasound.
Bassett says MRI can pick up more cancer by detecting areas of particularly high blood flow, which tumors need to grow.
Berg and her fellow researchers suggest in an editorial accompanying the JAMA article that the future of breast cancer screening will likely become far more tailored to the individual patient's level of risk.