Abstract PO3-02-06: Predictive Factors for adjuvant radiation use in patients &gt;70 years with pT1N0 HR+ breast cancers
Authors: Chennapragada Suma Sri , Shi Runhua , Sharma Shivani , Burton Gary 
Published: May 2024

Introduction: In 2004 the CALGB 9343 study reported that women &gt;70 years of age with pT1NO hormone receptor positive breast cancer received no meaningful benefit from breast irradiation following lumpectomy. Although there was a modest reduction in local recurrence, there was no improvement in rates of mastectomy for local recurrence, distant metastases, 5-year overall survival (OS) and breast cancer specific survival therefore concluding that it was reasonable to omit radiation therapy in this group. An update of the CALGB 9343 study in 2013 with 10-year follow-up came to the same conclusion. Previous analysis of the National Cancer Database (NCDB) and the SEER database showed, however, that the majority of women with these characteristics were still receiving radiation therapy. We conducted this retrospective analysis from NCDB to identify factors associated with the use of radiation in this population. Methods: We reviewed the NCDB database and collected records of all breast cancer patients aged &gt;70 years, who had hormone positive (HR+), pT1N0 disease between the years of 2004-2019. They were separated into radiation and non-radiation cohorts and then stratified based on ethnicity, age groups, insurance status, income quartiles, education quartiles, areas of residence, tumor size, comorbidities, diagnosis to treatment time, treatment facility type and geographic location. We then compared mortality between the two cohorts and completed a multivariate analysis to determine the demographic and clinical factors associated with the likelihood of receiving radiation. SAS was used for analysis and p-value &lt; 0.05 was deemed as statistically significant. Results: 147,611 patients met the criteria of age &gt; 70, pT1N0, HR+ treated with surgical lumpectomy. The majority of them were white, aged 70-75y, had Medicare, were in higher education and income quartiles and lived in metro areas (Table 1). 57.9% of the total study population received radiation. The possibility of receiving radiation decreased as age increased beyond 75 years. Uninsured patients, Medicare patients, those with comorbities, higher educational status as well as those who lived 20+ miles away from their treatment facility and treated at urban centers in central or south Atlantic areas were less likely to receive radiation. Those treated at Comprehensive community cancer programs and middle Atlantic areas were more likely to receive radiation. The possibility of radiation also progressively increased with tumor size. However, there were no differences observed when stratified by race, income status or chemotherapy use (Table 2). We also noted a small overall survival advantage for the radiation cohort (HR 0.77, p-value &lt; 0.0001) which could be explained by the fact that patients without comorbidities were more likely to receive radiation. Discussion: Our results provide a real-world estimate of radiation use in pT1N0 HR+ early-stage breast cancer in women &gt; 70 years. The major predictors of radiation use included younger age, low co-morbidities, insurance and institutions providing care. Lack of awareness about recent updates or concern about local recurrence could be contributing to the continued use of radiation. Although there are minor differences when stratified by demographics, it is concerning that the overall trend of radiation use has not significantly decreased over time. Since there is currently no data to support the routine use of radiation in this patient group as evidenced by randomized controlled trials, it is prudent to avoid radiation. This approach would help reduce healthcare costs, patient inconvenience and associated morbidity.

Table 1 Baseline characteristics

Table 2 Factors affecting radiation use

Citation Format: Suma Sri Chennapragada, Runhua Shi, Shivani Sharma, Gary Burton. Predictive Factors for adjuvant radiation use in patients &gt;70 years with pT1N0 HR+ breast cancers [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-02-06.