Advances in diagnostic imaging have led to general improvement in treating patients for various maladies. Recently, advances in breast diagnostic imaging with magnetic resonance imaging (MRI) in unselected patient populations have exposed a number of pitfalls that threaten well-established, data-proven medical practice. Recognition of these pitfalls should lead to clinical trials to resolve the more controversial issues and result in practice algorithms to support the use of breast MRI in targeted patient populations.
Diagnostic imaging with mammography has identified many more women with cancerous tumors smaller than 2 cm. Decrease in stage at presentation of these smaller tumors has led to a survival benefit beyond that expected by simple stage migration alone for patients with screen-detected cancer versus those whose cancers are detected by clinical examination.1
Decreases in mortality resulting from mammographic screening are estimated to be 46% and vary by the age of the cohort examined.2
Still, mammography misses about 20% of all breast cancer, particularly in young women with dense breast parenchyma.3Breast MRI
Advances in breast imaging with MRI have heightened sensitivity in breast cancer detection, though at increased cost: the sensitivity gained is plagued by significant variation in specificity, with most studies showing it to be inferior to that of screening mammography.4
Comparison of the specificity and sensitivity of MRI versus mammography in breast cancer screening has been studied primarily in women at high risk for developing breast cancer, such as BRCA gene carriers. Even in the groups where young age compromises the reliability of mammography, MRI has resulted in additional recall examinations in 10.7% of women, compared with 3.9% for mammography.5
In turn, these additional exams have led to a 3-fold increase in recommendations for biopsy (3.1% vs 1.3%). The increased cost of MRI, with its attendant increase in repeat exams and biopsies in high-risk populations, is likely to forestall its application to the routine screening of all women, where the putative marginal advantage of the sensitivity of MRI over that of digital mammography in the 50-year-or-older group may be slim.
The role of MRI in the management of patients newly diagnosed with breast cancer represents the area of controversy where the accumulated evidence of the past 30 years provides significant insight into the pitfalls associated with routine MRI use. It is here where MRI interpretation has the most significant impact, and a possibly deleterious effect on the care of the patient. To become fully aware of these pitfalls, we must review some of the remarkable progress made over the past 40 years in our understanding of the history of breast cancer and its treatment.Evolution of breast cancer management
In 2002, reports by Fisher6
affirmed the long-term validity of breast-conserving surgery (BCS) for the management of early-stage breast cancer (ESBC). More than a decade earlier (in 1991), a National Cancer Institute Consensus Conference had endorsed BCS—margin-clear lumpectomy with postoperative whole-breast irradiation—over mastectomy as the preferred treatment of ESBC. This recommendation has been strengthened by the accumulating biological and clinical evidence of the natural history of this disease in patients with a single breast cancer documented by mammographic evaluation. When patients with ESBC are treated with BCS or mastectomy, local recurrence rates are the same at 5% to 10%.8
As discussed previously, the success of BCS has come from the increased use of screening mammography and the concomitant early diagnosis of smaller tumors.