Breast-cancer-screening isn't like looking for a needle in a haystack. It's harder. It's like looking for needles in a big field of haystacks, where some of the haystacks have needles, while most don't, but you don't know which are which, so you have to look in all of them.
Mammography is the best technique available right now to look for breast cancers in women who don't have any symptoms. On average, screening mammograms correctly identify 80% to 85% of women who have cancer and about 90% of women who don't.
Even as debate continues about who should get mammograms — and when, and how often — researchers are working on a blizzard of new approaches to breast imaging in hopes of reducing the number of cancers that are missed and the number of false alarms that lead to unnecessary biopsies. Here's a look at some of the approaches under study.
The screening mammography we get today takes X-ray images — usually two of each breast — looking for abnormalities that can't be felt in a physical exam. These include small tumors and tiny deposits of calcium, called microcalcifications, which, in clusters, may be a sign of cancer.
It's harder for mammograms to find cancers in the dense breast tissue that is normal in young, premenopausal women, because dense tissue and cancerous tissue each look white on a mammogram. Fatty breast tissue — more common in older women — looks dark on a mammogram, so any white cancerous tissue stands out.
In digital mammography, which was approved by the Food and Drug Administration 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 — the Digital Mammographic Imaging Screening Trial (DMIST) — compared the accuracy of conventional and digital mammography on nearly 50,000 women. Results, published in 2005, showed that across the entire sample, 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 detection rates nearly doubled — from 4.1-4.5 per 1,000 women to 7.9 per 1,000 — at a diagnostic center in San Luis Obispo after the center switched to digital mammography.
Digital mammography has advantages: Images can be enhanced, and they're easier to store and transmit. An analysis of 5,000 DMIST participants found that the average breast radiation dose per view was 22% lower for digital mammography than for analog.
But digital mammography is not available everywhere. "And it's more important simply to get a mammogram than to wait to get a digital one," says Dr. Pulin Sheth, chief of breast MRI and assistant professor of radiology at USC's Keck School of Medicine.
When it comes to reading mammograms, evidence shows that two radiologists are better than one — improving detection rates by about 10% on average. Double-reading is standard practice in many European countries but is used only in 25% to 30% of U.S. readings.
Could a computer fill in for the second reader? In this approach, a radiologist reviews the mammogram. Then a detection device scans it, marking suspicious areas. The radiologist then compares his or her analysis with the computer's and decides if further evaluation is needed.
Research hasn't always found benefits from computer-aided detection, but a large clinical trial published in 2008 did. Among more than 31,000 women who had conventional mammograms in England, computer-aided detection identified 87.2% of breast cancers, pretty much on a par with double-radiologist readings.
Scientists have discovered that by adding the right kind of noise (interference) to a mammogram image, they can make the image clearer. In a study of 75 images published last year, researchers found they could detect cancers as well or better than mammography alone, while reducing the number of false alarms by as much as 36%.
First reported in 2007, digital tomosynthesis takes at least 11 X-ray images of the breast at different angles, which a computer combines into three-dimensional images.
While mammography pulls the breast away from the body and squeezes it between two glass plates, tomosynthesis uses just enough pressure to hold the breast still — so it doesn't hurt the way mammography can. And because it doesn't squeeze the breast, tomosynthesis doesn't create overlaps in tissue that hide cancers.
It also may result in fewer false alarms. In a study reported last year, radiologists interpreted images from 125 women, 35 who had cancer and 90 who did not. False-alarm recall rates were reduced by 30% by using both tomosynthesis and digital mammography instead of digital mammography alone.