Phase 2 Study of Pre-Excision Single-Dose Intraoperative Radiation Therapy for Early-Stage Breast Cancers: Six-Year Update With Application of the ASTRO Accelerated Partial Breast Irradiation Consensus Statement Criteria

Intraoperative radiation therapy (IORT) allows delivery of high-dose radiation at the time of lumpectomy, potentially sparing adjuvant daily radiation. A phase 2 study of pre-excision IORT was performed for early-stage breast cancer. Patients ≥ 48 years of age with invasive ductal carcinoma, ≤ 3 cm, and clinically node-negative were eligible for this study, which was approved by institutional review board. Ultrasound was used to select electron energy and cone size to cover the tumor plus 1.5- to 2.0-cm lateral margins and 1-cm-deep margins (90% isodose). Fifteen Gy was delivered with a Mobetron irradiator, and immediate needle-localized partial mastectomy followed. Local event results were updated using the Kaplan-Meier method. A total of 53 patients received IORT alone. Median age was 63 years, and median tumor size was 1.2 cm. Of these, 81% were positive for estrogen receptor or progesterone receptor, 11% were positive for human epidermal growth factor receptor 2, and 15% were triple-negative. Also, 42%, 49%, and 9% would have fallen into the Suitable, Cautionary, and Unsuitable groups, respectively, of the American Society of Therapeutic Radiation Oncology consensus statement for accelerated partial breast irradiation. Median follow-up was 69 months. Ipsilateral events occurred in 8 of 53 patients. The 6-year actuarial rate of ipsilateral events was 15% (95% confidence interval = 7%-29%). The crude event rate for Suitable and Cautionary groups was 1 of 22 (5%) and 7 of 26 (27%), respectively. Overall survival was 94.4%, and breast cancer-specific survival was 100%. The rate of local events in this study is a matter of concern, especially in the Cautionary group. On the basis of these findings, pre-excision IORT, as delivered in this study, may not provide adequate local control for less favorable early-stage breast cancers.