Use of breast MRI to distinguish treatment failure versus new primary tumor following single fraction breast intraoperative radiotherapy for breast cancer (SF-IORT).

Abstract

e12534 Background: Single-fraction, intraoperative radiation therapy (SF-IORT) can replace whole breast radiotherapy (WBT) in select patients after lumpectomy for breast cancer. By combining histology review with co-registration of breast MRI at diagnosis and following an in-breast tumor recurrence, we sought to characterize IBTR as: missed on initial MRI, treatment failure, or new primary tumor. This has important implications for both breast MRI and understanding the effectiveness of SF-IORT. Methods: We reviewed our IORT database for patients with IBTR. Three radiologists recorded findings on DCE-MRI, mammograms and ultrasound, pathology at initial diagnosis and IBTR, and time to IBTR. Results: 90 women received SF-IORT between 12/6/2002 - 4/10/2019. There were 6 IBTRs (average age at recurrence 63, range 49-71 years). For these 6 patients, initial diagnostic mammograms showed fatty (1), scattered (4) or extremely dense (1) breasts with suspicious masses (4), calcifications (1), or asymmetry (1), average size 1.4 cm: range 0.3 - 2.0 cm. On MRI, background parenchymal enhancement was minimal (2), mild (2), moderate (1), or marked (1), showing a mass (4), mass/distortion (1), or post-biopsy marker/no abnormal enhancement (1). Initial pathology showed 2 IDC, 3 IDC/DCIS, and 1 DCIS, (average size 1.7 cm, range 1.1 - 2.4 cm) with 6/6 ER +, 5/6 PR + and 6 HER2 negative. IDC Ki-67 ranged from 5-25%. 5/6 patients had sentinel lymph node biopsy (SLNB) with 1/5 having a positive SLN. 4/6 received endocrine therapy. One patient declined follow-up mammography. After IORT, IBTR (average size 1.4 cm, range 0.7 - 3.6 cm) was diagnosed by mammography (3), palpable breast lump (2), or palpable axillary lymph node (LN) (1) shown as mass (4), mass/calcifications (1), or abnormal LN (1). IBTR occurred post-SF-IORT an average of 141.7 months, range 88.3 to 195.8 months. 2/6 IBTR occurred near the biopsy cavity. Subsequent surgery included mastectomy (3), re-excision lumpectomy/RT (2), or axillary LN dissection/RT (1) showing 4 IDC, 1 IDC/DCIS, and 1 IDC /ILC (6/6 ER +; 3/6 PR positive; 2 PR weakly positive; and 5 HER2 negative, 1 HER2 equivocal). Ki-67 ranged from 1-70%. Conclusions: 6/90 (6.6%) patients had an IBTR an average of 141.7 months post SF-IORT with 2/6 near the biopsy cavity. Breast MRI reliably screens patients for SF-IORT. Co-registration of imaging can help distinguish true recurrences from new primary tumors.