Abstract PS1-63: A survey of radiation oncologists on contemporary axillary management in post-mastectomy breast cancer patients

Abstract Background: Local-regional treatment (LRT) of the axilla in breast cancer has evolved over the past several decades. The AMAROS trial demonstrated that dedicated axillary radiation therapy (aRT) can provide local control and allow for less invasive axillary surgery in select patients. Since the AMAROS data was published in 2014, there are no large-scale studies specifically analyzing how this data has impacted clinical practice. Methods: An anonymous case-based survey was sent to 4,254 Radiation Oncologists (RO) who identified as practicing physicians in the US as of May 2020. Those who identified that they do not treat breast cancer patients were excluded. The survey was conducted through the Qualtrics™ platform. Descriptive analyses were performed by the survey software and analytical statistics were performed using R (v4.0.2) utilizing ANOVA, t-tests, and chi-squared analysis. Results: A total of 293 RO completed the survey. Mean years in practice was 18.4 and most were in private practice (41.4%), followed by academic practice (28.2%) and hospital-employed (25.7%). Most (65%) reported that the type of post-mastectomy breast reconstruction does not influence their axillary treatment algorithm. Cases and responses are as follows: Case 1: A 57-year-old female with a cT1N0, ER-positive, Her2-negative breast cancer undergoes mastectomy and sentinel node biopsy (SLNB). Pathology reveals a T1 tumor with 2 of 3 sentinel lymph nodes with 2mm tumor deposits. The majority (75.4%) of RO reported they would proceed with aRT, while 8.7% preferred ALND alone, 7.1% elected for both aRT and ALND, 3.3% chose no further axillary therapy, and 4.5% needed more case information to make a decision. Treatment decision was dictated by clinical trial evidence (62.2%) and national guidelines (26.4%), but 11.2% reported their decision was largely impacted by clinical experience. The ACOSOG Z11 and AMAROS trials had the largest impact on clinical decision-making. For RO who chose to treat with aRT, AMAROS and MA-20 had the highest impact in determining radiation fields, and 88.7% would give RT to both the chest wall and axilla. Choice of axillary treatment did not differ by years in practice (p=0.54), percentage of breast patients treated (p=0.22), or by clinical practice setting (p=0.44). Case 2: A 69-year-old female with a cT1N0 ER/PR-negative, Her2-positive breast cancer undergoes mastectomy and SLNB. Pathology demonstrates a T1 tumor and 4 of 4 sentinel nodes with disease but without extra-nodal extension. Treatment results were mixed: 45.5% recommended both ALND and aRT, 38.5% chose aRT alone, and 14.3% recommend ALND alone. Most (85%) cited that their decision was based upon clinical trial evidence and/or national guidelines. MA-20 and AMAROS were cited as having the highest impact on the decision to perform aRT and determining RT fields. 96.2% of those recommending RT would treat both the chest wall and axilla. On average, RO who were in practice for a shorter period of time preferred both ALND and aRT, while those in practice for more years preferred that patients undergo either ALND or aRT alone (mean 12.9 vs 20.3 years, p<0.001). Treatment decision to undergo dual or single LRT was not associated with percentage of breast patients treated (p=0.41), or by practice setting (p=0.92). Conclusion: There remains significant heterogeneity in axillary treatment patterns for N+ breast cancer patients amongst RO in the US. Those patients with significant nodal burden (≥4+ nodes) were more likely to receive additional axillary therapy, and with combination LRT when treated by RO in practice for a shorter number of years. Physician education on clinical trial inclusion criteria and development of clearer axillary treatment guidelines can aid in appropriate identification of axillary de-escalation opportunities. Citation Format: Chandler S Cortina, Carmen Bergom, Morgan Ashley Craft, British Fields, Adam Currey, Amanda L Kong. A survey of radiation oncologists on contemporary axillary management in post-mastectomy breast cancer patients [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS1-63.