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NEWS & VIEWS |
"These new investigations expand our knowledge in a very important area, which is how to screen for breast cancer in very high-risk groups," said Robert Smith, PhD, Director of Cancer Screening for the American Cancer Society. "At this point in time, the amount of information we have is quite thin with respect to age to begin screening and the best way to screen in women who are at higher risk."
Annual screening with mammography is already recommended by the American Cancer Society and other organizations for women aged 40 and older at average risk of getting breast cancer. But for women at high risk—those with a strong family history of the disease or with a genetic mutation that predisposes them to breast cancer—that schedule may not be enough.
These women are at greater risk of developing breast cancer before age 40, when regular screening would ordinarily begin; or they may have cancers that grow very fast, developing in between mammograms. Moreover, mammograms are less effective in younger women because their breast tissue is denser, making the images harder to read. And in some cases, the types of tumors high-risk women develop are less identifiable by mammography.
ACS guidelines advise high-risk women to discuss with their doctor other screening methods—like MRI or ultrasound—that can be used to supplement regular mammography. Beginning screening at a younger age or screening more frequently are also options.
Mieke Kriege, MSc, of the Rotterdam Family Cancer Clinic at Erasmus Medical Center, and colleagues from a number of Dutch centers, recruited 1,909 women at increased risk for breast cancer because of a family history of the disease and/or a genetic mutation. The women were given a physical breast exam by a doctor every six months, and a mammogram and MRI scan every year.
Fifty breast carcinomas were found within a median follow-up period of 2.9 years. For 45 of these, sufficient data were available for comparison of mammography and MRI. MRI found 32 tumors, of which 22 were not visible on the corresponding mammogram. Overall, mammography detected 18 tumors, of which eight were not visible with MRI. Mammograms were better able to find cases of ductal carcinoma in situ (DCIS); five of six DCIS lesions were identified by mammogram. MRI found only one of six DCIS cases, but it was the one missed by mammography.
The tumors found in women who participated in this study were significantly smaller and less likely to have spread to axillary lymph nodes than those found in two age-matched control groups of women with breast cancer.
"Our study shows that the screening program we used, especially MRI screening, can detect breast cancer at an early stage in women at risk for breast cancer," wrote Kriege and colleagues.
They do not suggest, however, that MRI is an appropriate screening tool for women at average risk of developing cancer.
For one thing, the cost of MRI is about $1,000 to $1,500, compared to $100 to $150 for a mammogram. And MRI has a higher rate of false-positive results than mammography, leading to costs, discomfort, and anxiety associated with unnecessary follow-up procedures.
"In our study, screening by MRI led to twice as many unneeded additional examinations as mammography (420 versus 207) and three times as many unneeded biopsies (24 versus 7)," the researchers wrote.
Those drawbacks make MRI impractical for use on women who aren’t especially likely to develop breast cancer. For women at high risk, though, the trade off is more balanced.
"The fact that the rate of false-positives is higher [with MRI] is of very little consequence to women at high risk," said Smith. "Everyone would like to avoid a false positive, but the greater priority is to detect breast cancer early."
Although the findings are not definitive enough to make explicit recommendations that high-risk women begin screening at a particular age and with a particular method or combination of methods, Smith said, the study lends support to the ACS guideline for high-risk women to consider supplementing regular mammography with MRI.
"The current thinking is that mammography plus MRI offers greater advantages to younger, very high-risk women than either modality alone," he said. "The more we learn about which tumors MRI detects and which it does not detect, and how we account for failures in both modalities to detect breast cancer early, the greater the potential for establishing tailored [screening] regimens for high-risk groups that will be more effective."
Improving screening in this group of women could have important long-term implications, Smith noted. Many women who know they are at very high risk of developing breast cancer choose bilateral prophylactic mastectomy and/or oophorectomy to reduce the chances they will get cancer. Better screening could allow some women to choose more intensive surveillance, or postpone the decision about prophylactic surgery to a later time.
"The more we learn about early detection [in this group of women], the more we may gain confidence that more intensive, regular screening is a viable and perhaps even competing option to other, more difficult and nonreversible decisions such as prophylactic surgery," he said.
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