Clinical and Health Affairs
Breast MRI: Opportunities and Challenges
By Deborah Day, M.D.
Abstract
In 2007, the American Cancer Society published guidelines for using breast MRI to screen women who were at high risk for breast cancer. Although breast MRI, which is typically used as an adjunct to mammography, is highly sensitive for detecting breast cancers, its use is somewhat controversial for a number of reasons including its cost and lack of specificity. This article describes the indications for breast MRI and discusses the pros and cons of using it to screen women for cancer and evaluate the extent of disease in women who are newly diagnosed.
Breast cancer is the most common cancer diagnosed in women in the United States and the second most common cause of death from cancer among women in this country.1 Between 1975 and 1999, the incidence rate of invasive breast cancer rose progressively for U.S. women of all races.2 The rapid increase in the incidence rate of ductal carcinoma in situ (DCIS), the pre-invasive stage of breast cancer, during the 1980s and 1990s has been attributed to the increased use of mammography screening. The incidence rate of DCIS has since stabilized,1 and today, more than 20% of cancers are diagnosed as DCIS.3 The mortality rate for breast cancer also has fallen progressively during the last two decades because of increased use of screening mammography and better treatments for breast cancer.2
Screening mammography is currently the best tool we have for detecting breast cancer in the general population. It is a very good tool, but it is not perfect. Up to 20% of breast cancers are missed on mammography. One way to do a better job of not missing those cancers is to use mammography in conjunction with other diagnostic tools.
During the last decade, some have advocated for using breast magnetic resonance imaging (MRI) as an ancillary imaging tool for detecting breast cancer, as it has been proven to have 89% to 100% sensitivity for detecting invasive ductal breast cancer.4 Unlike mammography, breast MRI’s sensitivity is not impaired by dense fibroglandular tissue or scar tissue, tissue damaged by radiation therapy, or prosthetic breast implants or other types of breast reconstruction.4 In published studies comparing imaging modalities, MRI has proven to be superior to mammography and breast ultrasound in detecting invasive breast cancer (although it is not as good at detecting some other cancers).5-11 It is especially good at detecting high-grade DCIS, which accounts for approximately half the cases of DCIS.12 High-grade DCIS will almost always progress to high-grade invasive cancer. Therefore, mammography and MRI may be considered complementary in diagnosing DCIS, as about 10% of DCIS cancers are seen only on mammography, and up to 40% are seen only on MRI (usually high-grade DCIS that is not calcified).4
In 2007, the American Cancer Society (ACS) published guidelines for using screening breast MRI in high-risk women.13 This led to increased awareness of breast MRI in the general population and a further increase in its use. In a 2008 national survey, the Society of Breast Imaging found that 85% of the radiology practices that responded were doing breast MRI or planning to do it in the near future.14 Despite the growing use and acceptance of breast MRI, it is not without its critics.
Indications for Breast MRI
In the last eight to 10 years, radiologists have gained experience with breast MRI and more studies have been done on its effectiveness as an ancillary screening tool for detecting breast cancer. Thus, there is increased understanding about how and when to use breast MRI.
Breast MRI has several indications. Screening women at high risk for breast cancer is one. These are women who have a lifetime risk greater than 20% to 25%. Other reasons for using it include determining the extent of disease in a patient with newly diagnosed breast cancer, evaluating the response of breast cancer to neoadjuvant chemotherapy, problem-solving in women with inconclusive mammograms and breast ultrasounds, searching for mammographically occult primary breast cancer in a woman presenting with metastasis (Figure 1), and evaluating the integrity of silicone breast implants. At Abbott Northwestern Hospital’s Piper Breast Center in Minneapolis, we performed about 1,200 breast MRIs in 2008; about 40% involved screening high-risk women, another 40% were done to evaluate extent of disease in women with newly diagnosed breast cancer. Today, almost all women with newly diagnosed breast cancer who are seen at the center are being evaluated with breast MRI.
〉 Screening
The ACS recommends annual screening MRI (in addition to screening mammography) for women who have a life-time risk for breast cancer of greater than 20% to 25%. This high-risk group includes women who have a BRCA mutation or a first-degree relative who has one, a 20% to 25% or greater lifetime risk of developing breast cancer based on specific models, a history of therapeutic chest radiation to treat Hodgkin’s disease between ages 10 and 30 years, or who have a known propensity to develop breast cancer.13 Breast MRI screening has been shown to be effective in this relatively small patient population (Figure 2).13,15
The ACS guidelines raised new questions about who to screen and how. Determining breast cancer risk is complicated. Radiologists and primary care providers are ill-prepared to decide who should be assessed with breast MRI, who should do the assessment, and which tools should be used to determine risk. We are fortunate in the Twin Cities to have breast centers with high-risk clinics that can thoroughly and accurately make these determinations. However, in many parts of the state and country, women do not have access to such facilities. Once a woman is identified as being at high risk, she can undergo appropriate surveillance for breast and other cancers as deemed appropriate. She also can explore other options such as hormonal therapy or prophylactic surgery.
The ACS guidelines are even less helpful in determining which women at intermediate risk for developing breast cancer—that is, having a 15% to 20% lifetime risk of developing breast cancer—would benefit from MRI screening. Women at intermediate risk include those with a personal history of breast cancer, a weak family history (eg, postmenopausal breast cancer in one relative), or a high-risk lesion on breast biopsy such as lobular neoplasia or atypical ductal hyperplasia. The ACS does not recommend for or against breast MRI screening for those women. So the provider must decide if screening breast MRI is appropriate for a particular patient. These decisions are not straightforward, and a well-informed patient can put undue pressure on her provider to order a breast MRI when the indications are questionable.
The ACS recommends against MRI screening for women with a less than 15% lifetime risk of breast cancer, as the benefits in this population do not outweigh the risk of false-positive findings and additional imaging and biopsies.
Screening MRI of the contralateral breast is always performed when doing an MRI for local staging of newly diagnosed breast cancer. Mammographically occult breast cancer will be found in the contralateral breast in 3% to 4% of women.16,17 These are typically stages 0 to 1 breast cancers. Detecting these early cancers allows for treatment before they spread. Screening for them while staging the newly diagnosed cancer also allows for simultaneous treatment of both cancers. However, it has been argued that it is unlikely that these indolent cancers will become deadly before they become evident on routine mammography. It may be further argued that these cancers may be successfully treated with chemotherapy or hormonal therapy targeting the index cancer and that they may never become clinically significant.17 And it has been reported that about half of the abnormalities found in the contralateral breast are false-positives.17
〉 Determining the Extent of Breast Cancer
The greatest benefit of breast MRI is its sensitivity for detecting breast cancer. Early studies have shown that MRI of women with newly diagnosed breast cancer will often detect mammographically occult multicentric or multifocal cancer or much larger areas of involvement than are evident on a mammogram or breast ultrasound (Figure 3). A recent meta-analysis of the observational studies published to date has determined that the median prevalence of detection of additional foci in the ipsilateral breast is 16%.18 It would seem logical to assume that knowing more precisely the extent of disease prior to treatment could lead to better planning of tumor resection and improved surgical care. MRI may lead to a change in surgical treatment from lumpectomy to a larger lumpectomy or mastectomy up to 20% of the time. A recent meta-analysis of 13 observational studies showed that 8.1% of women were converted from lumpectomy to mastectomy and 11.3% from lumpectomy to wider local excision based on MRI findings.18 It has been the hope that more precise surgical planning would result in lower re-excision rates, lower recurrence rates, and eventually better survival rates. However, this may not be the case. In a recent study by Bleicher, re-excision rates were shown to have remained stable despite women having presurgical MRI.19 Bleicher also reported that recurrence rates have remained stable in women who have had presurgical MRI.19 It is too early to know about survival rates.
Areas of Controversy
Because breast cancer affects a large population and has significant psychological overlay, breast cancer screening is costly and controversial. When I first started doing breast imaging in the mid-1990s, the big question was whether we should be screening with mammography at all. Since then, we have wrestled with whether women between 40 and 50 years of age should receive screening mammography. We have also debated whether MRI is a valuable adjunct to mammography for certain women.
One concern is the relatively low specificity of MRI, resulting in more women having to go through additional diagnostic evaluation. Abnormal breast MRI studies must be followed up with second-look ultrasound and ultrasound-guided and MRI-guided breast biopsy. In MRI screening studies, call-back rates for additional imaging have ranged from 8% to 17%.10, 20-23 At the Piper Breast Center, we have a call-back rate of 14% for screening MRI compared with about 6% for screening mammography. The added imaging and biopsy evaluation may cause patients significant anxiety, increase costs, and prolong treatment. In addition, many sites that offer breast MRI do not have MRI biopsy capability, and sites that can do biopsies may not be able to interpret MRIs that were performed at other facilities. This often necessitates a repeat MRI at a facility that performs MRI-guided biopsy. Of the 2,404 women who had breast MRI at the Piper Breast Center between 2006 and 2008 for all indications, 26% (630) were recalled for further imaging evaluation. About two-thirds (408) of the women who were recalled had a biopsy. Cancer was found in 149 of these women (37% of the biopsies), resulting in a false-positive rate for breast MRI of about 20%.
A related concern is that breast MRI in women with newly diagnosed breast cancer can delay surgical treatment up to three weeks, as positive MRI findings may result in the need for time-consuming additional work-up with breast ultrasound and image-guided biopsy.19 Women and their surgeons must understand that the decision to treat breast cancer must be based on histology and not just on suspicious MRI findings. Findings on pre- surgical MRI (both true-positive and false-positive) also may cause more women to choose unnecessary mastectomy over the equally effective, less-invasive lumpectomy.19 These observations are raising questions about whether presurgical breast MRI in a woman with newly diagnosed breast cancer may cause more harm than good.
In addition to these concerns is the very real issue of cost. The charges for breast MRI range from $1,500 to $3,500, depending on whether the procedure is done in a hospital or clinic. This is five to 10 times the cost of a mammogram. It also must be noted that insurance companies require prior authorization for all breast MRIs but do not guarantee that the cost of the procedure will be covered even if it is authorized.
Future Developments
Women are becoming very educated about health issues. They are able to search the Web to learn about breast care. They are aware of their options and are their own advocates. Some women want to have a breast MRI even when they don’t meet the criteria. Therefore, it is important for health care providers to be able to articulate the pros and cons of breast MRI with their patients.
In light of the recent literature that has been published regarding the lack of improved margin status and recurrence rates, the increased mastectomy rates, and the delay in treatment because of workup of MRI findings in women with newly diagnosed breast cancer undergoing pre-surgical breast MRI, we at the Piper Breast Center are re-evaluating our policy of doing routine pre-surgical MRIs. Surgeons, oncologists, and radiologists are working together to develop criteria for using pre-surgical MRI so that we can continue to serve all of our high-risk patients appropriately and in a timely fashion.
The American College of Radiology will be rolling out its voluntary Breast MRI Accreditation Program at the end of 2009. This is similar in scope to its successful voluntary breast ultrasound and stereotactic biopsy programs. We hope this program will further strengthen attempts to standardize breast MRI and prompt sites that do not offer the full spectrum of follow-up for abnormal breast MRI findings to do so, as only those sites that have MRI-guided biopsy capability or that partner with a site that does MRI biopsies will be eligible for accreditation. MM
Deborah Day is a radiologist with Consulting Radiologists, Ltd. in the Twin Cities and medical director of Abbott Northwestern Hospital’s Piper Breast Center.
References
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