Abstract P4-12-04: Reconstructive outcomes among breast cancer patients receiving post-mastectomy radiation with protons versus conventional radiation

Background/Objectives: Increasing numbers of women are receiving postmastectomy radiation (PMRT) with proton beam therapy (PBT), but data is lacking regarding the impact of PBT versus conventional radiation on breast reconstruction. In this retrospective analysis, we compared the reconstructive outcomes of breast cancer patients receiving PMRT with either protons or conventional radiation therapy at our institution between 2011-2017. Methods and Materials: We performed a chart review of all patients who underwent PMRT after implant-based reconstruction. Patients that completed single and two-stage reconstruction were included in the sample. Patients that had an expander at the time of PMRT were excluded to minimize any bias introduced after PMRT in the planned second stage implant exchange procedure. Clinical characteristics including patient age, smoking history, diabetes, and body mass index (BMI) as well as cancer stage, surgical and axillary management, systemic therapy, and the dose and technique of radiation were collected for all patients. The primary endpoints of the study were the rate of any ipsilateral surgical re-intervention (ISP) and the rate of reconstruction failure, defined as implant removal without subsequent reconstruction. Results: One hundred and eighty patients were identified; 127 treated with conventional radiation and 54 treated with PBT. Median age at radiation was 44 years (range 20-79). There were no significant differences between the PBT and conventional radiation cohorts in regard to smoking history, diabetes, or BMI. Proton patients were more likely to have received radiation to the left chest wall, but there were no differences in incidence or timing of chemotherapy, extent of axillary surgery, or the use of immediate versus immediate-delayed reconstruction techniques (all p>0.05). The estimated incidence of any ipsilateral surgical re-intervention between the PBT and conventional radiation cohorts was: year-1 10%/11%, year-2 18%/19%, year-3 24%/24%, and year-4 26%/24% (HR 1.15, p= 0.643). Common reasons for surgical re-intervention included infection and capsular contracture and the latter reason was more prevalent in the proton group (see Table for details). A greater proportion of patients in the PBT group underwent explantation though a similar proportion of proton and photon patients experienced an ultimate reconstruction failure (11% vs. 12%, p=NS). Conclusions: Based on our preliminary analysis, patients receiving either PBT or conventional PMRT for locally advanced breast cancer demonstrated similar rates of surgical re-intervention and reconstruction failure after implant-based reconstruction. Additional analyses, examining differences by nuances of radiation technique, are anticipated. Prospective data is needed to further characterize reconstructive outcomes between the two treatment modalities. Citation Format: Rachel B. Jimenez, Emily Melick, George Naoum, Beow Yeap, Andrew Johnson, Kassandra Nealon, Eric C. Liao, Shannon M. MacDonald, Alice Y. Ho, Alphonse G. Taghian. Reconstructive outcomes among breast cancer patients receiving post-mastectomy radiation with protons versus conventional radiation [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-12-04.