ASTRO suitability criteria assessment in early-stage breast cancer patients treated with intraoperative radiation therapy (IORT) plus 21 gene recurrence score (RS) assay result guided adjuvant medical therapy.

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e12598 Background: A patient subset consented in an institutional review board-approved single institution clinical trial designed to determine the efficacy and outcome of single fraction IORT received adjuvant medical therapy recommendations based on their RS results. Patients were categorized according to American Society for Radiation Oncology (ASTRO) suitability criteria for accelerated partial breast irradiation. Comparison was made between ASTRO suitability criteria, RS and post-IORT outcomes. Methods: Outcome of pts completing single fraction (20Gy) IORT per protocol using disposable balloon electronic brachytherapy and RS assessment were reviewed. Data collection included demographics, pathology, RS, medical therapy, local (LR) and axillary (AR) recurrences, and survival. Results: From Nov 2011 – Jan 2016, 115 pts (aged 43 – 84, mean 63 years) completed both IORT per protocol and RS assessment. Pts with estrogen receptor positive invasive carcinomas (range 0.2 – 2.4 cm, median size 0.9 cm) and RS results were categorized by ASTRO suitability criteria, LR and AR, as shown in Table 1. The recurrence rate at mean follow-up of 6.8 years was 3.5%. There were 3 LR (RS 0, 17, 18) and 1 AR (RS 19). There has been no breast cancer related death. Adjuvant endocrine therapy was recommended to all pts. Twenty-three (20%) patients received chemotherapy, including 12 (71%) pts in the high RS (RS >25) groups. Chemotherapy was not given to any pt with a RS <18. One LR (RS 0, ASTRO Suitable, age 65, 1.5 cm) declined endocrine therapy. Ten (19%) pts with RS of 11 – 25 received chemotherapy. One LR (RS 17, ASTRO suitable, age 64, 1.5 cm) and 1 axillary recurrence (RS 19, ASTRO Suitable, age 66, 1.3 cm), neither receiving chemotherapy, were compliant with endocrine therapy. One LR (RS 18, ASTRO Suitable, age 51, 0.6 cm) was treated with cyclophosphamide and docetaxel. Seven (78%) pts with RS of 26 - 30 and 5 (63%) pts with RS >30 received chemotherapy, with no recurrences in these groups. Conclusions: One hundred fifteen pts treated with single fraction IORT per protocol and RS guided adjuvant medical therapy at a single institution were found to have a 3.5% recurrence rate at mean follow-up of 6.8 years. ASTRO suitability criteria and high RS results (RS > 25) did not correlate with recurrence. The success of IORT observed in this trial as local therapy for early-stage breast cancer patients was independent of genomic factors or patient suitability criteria. Recurrence rates were comparable to those reported in IORT peer-reviewed published data and treatments using breast conserving surgery plus whole breast radiation therapy. [Table: see text]