Impact of breast MRI in women eligible for breast conservation surgery and intra-operative radiation therapy

Purpose: The current standard of care for women diagnosed with early stage breast cancer is breast-conserving surgery (BCS) followed by external beam radiation therapy, commonly delivered over 3-6 weeks. As an alternative, select patients can undergo intra-operative radiation therapy (IORT) at the time of BCT. This technique delivers a single fraction of radiation at the time of surgery, enabling patients to undergo both surgery and radiation in a single session. Our current study analyzed the value of incorporating breast MRI into the routine work-up of patients deemed eligible for IORT, to quantify the impact on patient eligibility and requirement for additional work-up.

Materials and methods: We retrospectively identified patients treated by a single surgeon who were eligible for IORT based on institutional eligibility criteria which included: women age ≥55, grades 1-2, size <3 cm, estrogen receptor (ER) positive, Her-2 neu non-amplified and low/intermediate Ki-67, unifocal invasive ductal/mixed histology carcinomas. All patients must have undergone a physical exam and bilateral diagnostic mammography with ultrasound. From this population, we identified all patients who had undergone bilateral breast MRI as part of pre-operative evaluation.

Results: A total of 215 women were identified who met all eligibility criteria. MRI detected additional abnormalities in the breast in 89 patients (41%). Sixty-eight women underwent additional biopsies, with a total of 117 separate lesions biopsied. Of these, pathology was benign in 61 (52.1%), atypical ductal hyperplasia (ADH) in 21 (18%), ductal carcinoma in-situ (DCIS) in 17 (14.5%) and invasive disease in 18 (15.4%). Six patients had MRI-detected abnormalities in the contralateral breast only, with biopsies identifying invasive disease (3), DCIS (1) and benign (2) findings. MRI showed abnormalities in both breasts in 6 patients and 18 additional lesions were biopsied which reveled invasive carcinoma (6), DCIS (7), ADH (3) and benign findings (2). Fifteen patients had either multifocal/multicentric disease or index lesion >3 cm on MRI and were deemed ineligible for IORT. Based on either MRI size or biopsy results, management was ultimately changed for 27 patients (12.5%). Extramammary findings were observed in 17 patients and 11 of these patients underwent further imaging studies all of which returned negative results.

Conclusion: Preoperative bilateral breast MRI is a valuable tool in the proper selection of patients best suited for IORT. Even in highly selected, favorable risk patients, MRI detected additional lesions that changed surgical and radiation therapy recommendations in 12.5% of patients. However, the cost/benefit ratio needs to be taken into consideration given the high frequency of benign biopsies and additional radiological work-up.