2654 - Over Treatment of Stage I, Node-Negative, Hormone-Sensitive Breast Cancer? Analysis of Techniques and Doses at a Comprehensive Cancer Center with Community Network Affiliates

J. G. Bazan Jr¹, S. Yoon², P. Wu², B. Eastman¹, C. L. Gomez², B. Cahan³, G. Green⁴, S. M. Glaser¹, A. L. Schwer⁵, J. H. Kim⁴, H. K. Chen⁶, M. E. Simental⁷, E. H. Radany¹, and W. T. Watkins²; ¹Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, ²City of Hope, Duarte, CA, ³City of Hope National Medical Center, Department of Radiation Oncology, Duarte, CA, ⁴City of Hope, Torrance, CA, ⁵Department of Radiation Oncology, Lennar Comprehensive Cancer Center, City of Hope National Medical Center, Irvine, CA, ⁶Department of Radiation Oncology, City of Hope, South Pasadena, CA, ⁷Valley Radiotherapy Associates, Beverly Hills, CA, United States

Purpose/Objective(s): Accelerated partial breast irradiation (APBI) is an alternative to whole breast irradiation (WBI) in many patients and decreases burden of care and toxicities. Since 2017, consensus guidelines have stated that APBI is an accepted treatment option for patients =50 years old with stage I (pT1 pN0) hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) invasive breast cancer (BC). Evidence suggests diminishing benefits of lumpectomy cavity boost (LC-B) with age >50, accompanied by increased toxicity. In 2020, the pandemic coupled with publication of long-term results of a once daily external beam APBI (EB-APBI) regimen changed the landscape of treatment delivery for low-risk BC patients. We hypothesize that EB-APBI use has increased and LC-B use has decreased since March 2020 but that EB-APBI remains underutilized and LC-B use overutilized in a comprehensive cancer center main campus (MC) and network (Nw) affiliates. Materials/

Methods: We used a computer algorithm to identify low-risk stage I BC patients (age =50 y; pT1N0; grade 1-2; HR+/HER2-; negative margins) treated with lumpectomy+radiation from 1/2017-present and confirmed eligibility for each patient. Data collected included patient demographics, treatment location (MC v. Nw), treatment technique (intraoperative radiation therapy [IORT], EB-APBI, WBI), dose and fractionation, and LC-B use in WBI patients. The modern era was defined as patients treated from April 2020 onwards (vs. 1/2017-3/2020). Chi-square tests were employed for group comparisons (p<0.05 significant).
Results: We identified 1403 patients of which 1215 met all criteria. The age distribution was 24% age 50-59 yr; 44% age 60-69 yr; 32% age =70 yr. The majority (79%) were treated at Nw sites and during the modern era (76%). Overall, 83%(N=1007) were treated with WBI, 12%(143) with EB-APBI and 5%(65) with IORT. The rate of APBI (EB-APBI or IORT) was not statistically different in the pre-modern vs. modern era (16% vs. 17%, p=0.64) due to higher rates of IORT use in the pre-modern vs. modern era (15% vs. 2%, p<0.0001). EB-APBI use significantly increased from 1% to 15% (p<0.0001). In the 1150 non-IORT patients, the rate of EB-APBI use was 12% overall (1% pre-modern era vs. 16% modern era, p<0.0001) and was significantly higher at MC compared to Nw (31% vs. 9%, p<0.0001). Use of EB-APBI varied with age: 7% age 50-59 y vs. 13% age 60-69 y vs. 17% age =70 y (p=0.001). In patients receiving WBI (N=1007), use of LC-B decreased (84% pre-modern vs. 76% modern era, p=0.01). LC-B use varied by age: 90% age 50-59 yr vs. 75% age 60-69 yr vs. 71% age =70 yr (p<0.0001).
Conclusion: We found significant increase in EB-APBI use and decrease in LC-B use across time. The observations that <20% of patients =70 y receive EB-APBI, <10% of patients in our Nw receive EB-APBI, <10% of patients aged 50-59 y receive EB-APBI, and >70% of patients in all age groups receive LC-B suggest that we have an opportunity to decrease the burden of care for this favorable patient population.