Factors Affecting MRI Accuracy in Breast Cancer
Abstract & commentary
By William B. Ershler, MD
Synopsis: Age and HER2 status were shown to independently affect MRI accuracy in defining residual disease after neo-adjuvant systemic therapy for locally advanced breast cancer.
Source: Moon H-G, et al. Age and HER2 expression status affect MRI accuracy in predicting residual tumor extent after neo-adjuvant systemic treatment. Ann Oncol. 2009;20: 636-641.
Neo-adjuvant systemic treatment (NST) is now commonly utilized for patients with locally advanced breast cancer (LABC),1 as it has been shown to improve breast conservation rates without compromising oncologic outcomes.2 However, treatment responses are variable. Some tumors shrink concentrically to form a single foci of residual tumor cells, whereas others leave scattered tumor cells in patchy patterns, rendering evaluation of NST response imprecise. The difficulties in delineating tumor extent after NST can result in inadequate resection with both cosmetic and survival consequences.
Recent studies suggest breast magnetic resonance imaging (MRI) to be an accurate diagnostic tool for evaluating the extent of residual disease after NST.3,4 Accordingly, MRI has become generally used to assess NST response for those with locally advanced breast cancer.5 Yet, although superior to ultrasound and mammography, MRI still has certain rates of over- or under-estimation, most likely influenced by tumor response, chemotherapeutic agent, or NST-induced reactive changes within the tumor.5
Thus, Moon et al from Seoul National University proposed that there might be tumor or patient characteristics that would predict the accuracy of MRI to accurately define post-NST treatment. They correlated clinicopathological and molecular profiles of breast cancer patients with MRI accuracy, as determined at surgery after completion of NST.
From January 2006 to February 2008, 195 patients received NST and preoperative MRI. Overall, MRI predicted residual tumor extent with higher accuracy than ultrasonography. Triple-negative (TN) tumors showed highest correlation between MRI-measured and pathologic tumor size (r = 0.781) when compared with other subtypes. Multivariate analysis showed age and HER2 expression status as independent factors predicting MRI accuracy. When patients were classified based on their age and HER2 status, relatively older patients (> 45 years) with HER2-negative tumors showed the highest MRI accuracy. This finding was further validated using an independent cohort of 63 consecutive patients.
Commentary
Accurately defining the extent of residual disease after NST allows confidence that the surgical intervention to be undertaken will be optimal. A scattered pattern of tumor response after NST makes it difficult for surgeons to assess the extent of surgery, especially during breast conservation. This, in turn, may lead to repeated surgery on the basis of positive margins or an increased risk for ipsilateral breast tumor recurrence. Although a recent meta-analysis suggested that NST in operable breast cancer does not hamper the local control of disease,6 data from prospective clinical trials often give rise to the concerns of increased IBRT after NST.7,8 At the very least, it is plausible that ipsilateral recurrence after NST can be accounted for by the remaining cancer cells from inadequate surgery. In fact, a multifocal or breakup pattern of residual disease has been shown to be associated with increased locoregional recurrence.9
On the other hand, there is concern that overestimating residual tumor is also problematic, since it can lead to unnecessary mastectomies. Therefore, accurate preoperative determination of residual tumor extent after NST is a critical factor for optimal surgical management. In this regard, the results from this study are informative. First, they confirm that breast MRI is the most accurate method of predicting residual tumor extent after NST; a finding that had been previously reported.3,4 Furthermore, the study went on to identify that for younger patients and for those with HER2-positive tumors, the accuracy of MRI is significantly reduced. This observation may guide a more tailored approach in using MRI in breast cancer patients undergoing NST.
References
1. Kaufmann M, et al. Recommendations from an international expert panel on the use of neoadjuvant (primary) systemic treatment of operable breast cancer: an update. J Clin Oncol. 2006;24:1940-1949.
2. Buchholz TA, et al. Statement of the science concerning locoregional treatments after preoperative chemotherapy for breast cancer: a National Cancer Institute conference. J Clin Oncol. 2008;26:791-797.
3. Partridge SC, et al. Accuracy of MR imaging for revealing residual breast cancer in patients who have undergone neoadjuvant chemotherapy. AJR Am J Roentgenol. 2002;179:1193-1199.
4. Yeh E, et al. Prospective comparison of mammography, sonography, and MRI in patients undergoing neoadjuvant chemotherapy for palpable breast cancer. Am J Roentgenol. 2005;184:868-877.
5. Orel S. Who should have breast magnetic resonance imaging evaluation? J Clin Oncol. 2008;26:703-711.
6. Mieog JS, et al. Neoadjuvant chemotherapy for operable breast cancer. Br J Surg. 2007;94:1189-1200.
7. Charfare H, et al. Neoadjuvant chemotherapy in breast cancer. Br J Surg. 2005;92:14-23.
8. Rastogi P, et al. Preoperative chemotherapy: updates of National Surgical Adjuvant Breast and Bowel Project Protocols B-18 and B-27. J Clin Oncol. 2008; 26:778-85.
9. Chen AM, et al. Breast conservation after neoadjuvant chemotherapy: the MD Anderson cancer center experience. J Clin Oncol. 2004;22:2303-2312.
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