Preoperative magnetic resonance imaging (MRI) scans were not associated with a reduction in positive margins at the tumor site or in the need to reoperate to help ensure complete tumor excision in patients with breast cancer undergoing lumpectomy, according to new findings presented by Cairns et al at the 24th American Society of Breast Surgeons Annual Meeting. Because many physicians routinely order MRI scans prior to surgery, under the assumption that the images will help more precisely visualize the extent of a patient’s tumor than intraoperative imaging or the surgeon’s assessment, these findings may signify the need for new approaches to minimizing the rate of reoperations.
Background
“MRI exams are costly and potentially stressful for patients,” explained senior study author Marissa Howard-McNatt, MD, FACS, FSSO, Professor of Surgery and Director of the Breast Care Center at Wake Forest Baptist Health. “The thought is that they will help physicians achieve negative margins during the initial surgery. However, our study shows this is simply not the case,” she added.
A successful lumpectomy procedure calls for excision of the cancerous tumor as well as some of the surrounding healthy tissue to minimize residual disease. Tumor cavity shaving—involving the removal of additional tissue around the initial tumor cavity during a first operation—has often been shown to be extremely effective in eliminating a second surgery. If postsurgical pathology reports identify cancerous cells in the tumor margins, patients are advised to undergo another surgical procedure to remove additional tissue and clear the margin.
“Reoperation can be traumatic, and researchers continue to look for better ways to assess margin status while the patient is still on the operating table,” Dr. Howard-McNatt noted. “However, our study found that presurgical planning based on MRI images is not useful to achieve this goal and not a productive use of health-care resources,” she stressed.
Study Methods and Results
In the new study, investigators evaluated the tumor cavity-shaved margins of 631 patients from two previous randomized trials with a median tumor measurement of 1.3 cm in order to determine whether MRI scans were associated with a lower rate of positive margins. The investigators analyzed data collected at the time of surgery—prior to any additional cavity shaving—and after surgery to determine the final pathologic results.
Among the patients involved in the study, 26% (n = 165) had palpable tumors, 7% (n = 44) had invasive lobular histology, 32.8% (n = 207) had an extensive intraductal component, and 6.5% (n = 41) had been treated with neoadjuvant chemotherapy. MRI scans had been performed in 30.6% (n = 193) of the patients, with 31.1% (n = 60) of these patients later found to have positive margins. Among the patients who did not receive MRI scans, 38.8% (n = 170) of them had positive margins. However, the difference did not achieve statistical significance.
Conclusions
“In our study, MRI [scans were] in no way associated with clear tumor margins,” emphasized Dr. Howard-McNatt. “Perhaps surprisingly, we did find that tumor size was predictive of margin status. However, this may be attributable to an inaccurate initial assessment of the extent of the actual tumor size for a variety of reasons. For example, tumors may be discontinuous or have satellite lesions which may touch the edge of a specimen,” she said.
The investigators indicated that MRI scans may still be a valuable tool in many other preoperative breast cancer applications—including evaluation of patients with lobular breast cancer, known genetic mutations, and extremely dense breasts.
“No one wants to take a patient back to the operating room. Advances in surgical techniques and technology, including new imaging modalities such as contrast-enhanced mammography, may prove successful in adding precision to breast cancer surgery,” Dr. McNatt concluded.
Disclosure: For full disclosures of the study authors, visit breastsurgeons.org.
