Abstract PO3-22-03: Effect of Radiation Therapy on Survival Outcomes in Elderly ER/PR Positive AJCC Stage T1 Breast Cancer Patients
Authors: Shi Runhua , Burton Gary 
Published: May 2024

Abstract
Background: The CALGB 9343 study in 2004 reported that women &gt;70 years of age with pT1NO hormone receptor positive breast cancer received no meaningful benefit from breast irradiation following lumpectomy. The effectiveness of adjuvant radiation therapy in node negative, T1 tumor patients has been limited to institutional experiences with relatively lack of information in population-based studies. In this hospital-based study using National Cancer Data Base (NCDB) from 2004 to 2020, we report on adjuvant radiation therapy (XRT) usage and the survival outcomes in stage IA, IB, IC breast cancer patients who received XRT versus those who did not. Materials and Methods: Patients in the National Cancer Database (NCDB) who were registered between 2004 and 2019 and followed up to the end of 2020 were used in this research. We evaluated a cohort of 126,156 female breast cancer patients of age &gt;= 70 years with the American Joint Committee on Cancer (AJCC) stage TIA, TIB, and TIC. All patients were ER/PR positive, received hormonal therapy, all patients were either white or black, were either privately or Medicare insured, received hormonal therapy, and patients were receipt of adjuvant chemotherapy or not. Radiation statuses were grouped as no radiation, radiation only and/or radiation with boost. Other adjusted variables included: age, race, Charlson comorbidity index, payer status, income, education, distance traveled, diagnosing/treating facility, location of treatment and treatment delay. SAS for Windows 9.4 was used for all data management and statistical analysis. Multivariate Cox regression was used to assess the effect of the XRT on overall survival while adjusting for other factors. All p-values &lt; 0.05 or 95% Confidence Limits of Hazards Ratio (HR) does not include 1 were considered statistically significant. Results: Among 126,156 female breast cancer patients, the age distribution was 47.87%, 31.72%, and 20.4% for age group of 70-74, 75-79, 80 or older, respectively. Ninety-three percent of patients were white. 89% of patients were Medicare and 11% were privately insured at diagnosis. 21% of patient were with the Charlson Comorbidity index score 1 or above. 10.77%, 34.42% and 54.81% of patients were AJCC Stage T1A, T1B, and T1C respectively. 11.7% of patients received chemotherapy and 57.9% of patients received radiation therapy. 54.38%, 59.59%, and 57.59% of T1a, T1b, and T1c patients received the XRT, respectively. In univariate analysis, the XRT demonstrated a statistically significant increase of 10-year survival by 9.75%, 9.8%, and 12.6% in T1a, T1b, and T1c (all p &lt; 0.0001) patients respectfully.
In multivariate cox regression analysis, age was a predictor of survival outcome with a HR at 1.65, 3.02 for 75-79, and 80 or older as compared to 70-74 years old, respectively. In addition, compared to patients who traveled less than 20 miles, the HR were 0.90 for patients travelled more than 20 miles. AJCC stage was also associated the survival, a HR of 1.05 (95% CI: 1.01-1.186) for T1b, 1.16 (95% CI: 1.11 – 1.21) for T1c as compared for T1a. Adjusting for other factors, the usage of radiation reduced the risk of dying by 25% (HR=0.75, 95% CI: 0.73-0.77) when compared to no radiation therapy.
Conclusion: The current study has demonstrated that more than 54% of these patients received radiation therapy. In univariate analysis, the benefit of adjuvant radiation therapy is more than 9.7% for T1a, T1b, and T1c on 10-year overall survival which is statistically significant. Adjusting for other factors, patients receiving radiation therapy in these elderly population have a 25% less chance of dying as compared to no radiation therapy regardless of AJCC Stage. A further propensity score matching method would help assess the effectiveness of radiation therapy on these patients’ population. A randomized prospective clinical trial would be better to define the precise benefit of adjuvant radiation therapy in this elderly population.
Table 1 Patients Demographic, Social Economic and Clinical Characteristics XX- XX
Table 3 Hazard Ratios estimate from Multivariate Cox Regression XX- XX Radiation Effect on Overall Survival of Elderly Breast Cancer Patients by Stage T1A, T1B, T1C
XX- XX
Citation Format: Runhua Shi, Gary Burton. Effect of Radiation Therapy on Survival Outcomes in Elderly ER/PR Positive AJCC Stage T1 Breast Cancer Patients [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 PO3-22-03.