The role of magnetic resonance imaging as an imaging tool to assess disease status and residual disease in locally advanced breast cancer

Magnetic resonance imaging (MRI) is a very sensitive diagnostic tool for the evaluation of breast cancer. A MRI is more frequently utilized in conjunction with other diagnostic modalities, particularly mammogram, to better assess a breast abnormality or biopsy-proven cancer, including ductal carcinoma in situ (DCIS) [1]. Most recently it has also been demonstrated to be a better screening tool for women at high risk for developing breast cancer, including women with documented genetic predisposition. Because MRI has the advantages of providing a three-dimensional view of the breast, it has been shown to be more precise than standard imaging in determining the initial staging and evaluation of the extension of invasive disease [2]. This information is of particular value in patients with locally advanced disease, including inflammatory breast cancer (IBC) and in classic lobular histology, which may exhibit diffuse involvement of the breast at initial presentation and therefore are frequently treated with primary systemic therapy (PST) [3, 4]. The management of primary breast cancer has evolved significantly in the past decade, with the increasing use of preoperative or primary chemotherapy (PST), and most recently also primary hormonal therapy for both early and locally advanced breast cancers (LABCs). The advantages of the early use of systemic therapy are considered: the feasibility of a more conservative surgery, and the possibility of true in vivo testing of the tumor's drug sensitivity. The amount of residual disease found following surgical excision represents the pathological response to the preoperative treatment and remains the most important prognostic factor.

The high staging accuracy of breast MRI makes it an attractive method for assessing tumor response to PST. MRI can contribute in several ways to the management of patients receiving preoperative chemotherapy, including the initial determination of extent of disease for proper staging (baseline evaluation), early identification of poor responders (intermediate evaluation during treatment), and identification and description of the presence and extent of residual disease for surgical planning (preoperative imaging study) [3, 4]. MRI measurements of tumor response may have predictive value for disease recurrence and responsiveness to novel therapeutics. Comparison of dynamic parameters (e.g. signal enhancement ratio) at baseline and at subsequent evaluation time points can also contribute information on the response to treatment and predict residual disease [4]. A series of prospective trials has been conducted in patients with LABC, including IBC. Most recently a large multicenter trial sponsored jointly by the American College of Radiology Imaging Network, the Cancer and Leukemia Group B, and the National Cancer institute is integrating serial MRI tumor measurements with serial collection of tissue for evaluation of biomarkers (expression, genomic, protein arrays, as well as specific immunohistochemical markers and fluorescence in situ hybridization). The goal of such studies is to compare tissue assessment of biomarkers with imaging to identify the most appropriate tool for prediction of pathological response to PST. This study could impact on the present management of primary breast cancer by allowing the early introduction of novel therapeutics in patients with early demonstration of poor response to treatment.