Preoperative breast magnetic resonance imaging in early breast cancer: implications for partial breast irradiation

Accelerated partial breast irradiation (APBI) of patients with early breast cancer is being investigated on a multi-institutional protocol National Surgical Adjuvant Breast and Bowel Project (NSABP) B-39/RTOG 0413. Breast magnetic resonance imaging (MRI) is more sensitive than mammography (MG) and may aid in selection of patients appropriate for PBI.

Patients with newly diagnosed breast cancer or ductal carcinoma in situ (DCIS) routinely undergo contrast-enhanced, bilateral breast MRI at the Cleveland Clinic. We retrospectively reviewed the medical records of all early-stage breast cancer patients who had a breast MRI, MG, and surgical pathology data at our institution between June of 2005 and December of 2006. Any suspicious lesions identified on MRI were further evaluated by targeted ultrasound +/- biopsy.

A total of 260 patients met eligibility criteria for NSABP B-39/RTOG 0413 by MG, physical exam, and surgical pathology. The median age was 57 years. DCIS was present in 63 patients, and invasive breast cancer was found in 197 patients. MRI identified suspicious lesions in 35 ipsilateral breasts (13%) and in 16 contralateral breasts (6%). Mammographically occult, synchronous ipsilateral foci were found by MRI in 11 patients (4.2%), and in the contralateral breast in 4 patients (1.5%). By univariate analysis, lobular histology (infiltrating lobular carcinoma [ILC]), pathologic T2, and American Joint Committee on Cancer stage II were significantly associated with additional ipsilateral disease. Of patients with ILC histology, 18% had ipsilateral secondary cancers or DCIS, compared with 3% in the remainder of histologic subtypes (P = .004). No patient older than 70 years had synchronous cancers or DCIS detected by MRI.

Breast MRI identified synchronous mammographically occult foci in 5.8% of early breast cancer patients who would otherwise be candidates for APBI.