Patterns of Regional Radiotherapy Following Breast Conserving Surgery in Hormone Receptor Positive Breast Cancer with Limited Nodal Disease: A Single Institutional Experience

Abstract

<h3>Purpose/Objective(s)</h3> Since the publication of ACOSOG Z0011 in 2010, and the subsequent analysis of its radiation field design in 2014, there has been controversy about the extent of regional radiotherapy (RT) for patients with early-stage breast cancer found to have limited axillary nodal disease at time of breast conserving surgery (BCS). Furthermore, the MA.20 and EORTC 22922/10925 trials, both published in 2015, found that the addition of regional nodal RT to the internal mammary nodal chain (IMN) and upper axillary nodes including the supraclavicular region (SCV) demonstrated a reduction in regional and distant recurrences. Given the varying acceptable options for regional RT in this patient population, we sought to characterize the practice patterns at our institution. <h3>Materials/Methods</h3> Retrospective data from 2001-2021 were reviewed from a single provider to eliminate inter-provider variation. Included patients had estrogen receptor positive, HER2-negative breast cancer, and were found to have 1-3 positive axillary lymph nodes (LN) at time of upfront BCS. Univariate analyses were conducted to describe variations in treatment patterns. <h3>Results</h3> When divided by dates of diagnoses from 2001-2010 (n=82), 2011-2014 (n=44), and 2015-2021 (n=88) based on the publication of the landmark trials listed above, several significant trends were seen. There was a significant shift in radiation target, with a decrease in treating breast alone in favor of treating the breast + low axilla (Table 1). For patients in whom nodal irradiation was used, there was a significant increase in the inclusion of the IMN (0%, 9.1%, 25.0%; p<0.001). There was an increase in the utilization of sentinel LN biopsy resulting in a decrease in the median number of LN removed (11, 5, 3, respectively; p<0.001). This resulted in an increase in the mean ratio of positive LN to total LN removed (0.19, 0.39. 0.51, respectively; p<0.001). For patients treated from 2011-2021, those who received radiation to the SCV +/- IMN had larger tumors (mean 2.42 vs 1.75 cm, p=0.003), higher rates of ≥2 positive LN (40.8% vs 8.43%, p<0.001), and more lymphovascular invasion (60.5% vs 27.4%, p=0.002) compared to those who received radiation to the breast +/- low axilla. <h3>Conclusion</h3> Radiation target volumes have evolved over time in response to the publication of multiple randomized trials comparing different surgical approaches and radiation techniques. There is still significant heterogeneity, especially in treating patients with low-risk, node-positive breast cancer. Thus, future randomized control trials should consider enrolling patients across a broad range of radiation target volumes to align with contemporary treatment patterns.