OR08-06 Adjuvant Radiation Therapy Is Not Associated With A Survival Benefit After R0 Resection In Non-Metastatic Adrenocortical Carcinoma

Abstract Disclosure: Y.J. Lee-Saxton: None. C.E. Egan: None. T.E. Marshall: None. A. Tumati: None. T. Beninato: None. R. Zarnegar: None. T.J. Fahey: None. B.M. Finnerty: None. Introduction: The benefit of adjuvant radiation therapy (RT) in adrenocortical carcinoma (ACC) is not well characterized, particularly for those who undergo initial R0 surgical resection without evidence of metastatic disease. We aimed to identify factors associated with administration of adjuvant RT in these patients, and to determine the association between adjuvant RT and overall survival in patients with non-metastatic ACC who underwent R0 surgical resection. Methods: The National Cancer Database was queried for histologic codes denoting ACC from 2004-2018. Patients who underwent R0 resection without evidence of metastatic disease were included and placed into two cohorts - those who underwent adjuvant RT and those who did not. Patients with incomplete or unknown data regarding clinically relevant variables were excluded from analysis. A multivariable logistic regression was performed to identify predictors of adjuvant RT administration. A multivariable Cox regression was performed to identify factors associated with overall survival (OS). Kaplan-Meier survival estimates and log-rank test were also performed to assess the impact of adjuvant RT on OS. Results: 388 patients were identified: 51 (13.1%) patients received adjuvant RT, while 337 (86.9%) did not. Adjuvant chemotherapy administration was the only factor associated with administration of adjuvant RT (OR 6.45, 95% CI 3.02 - 13.8, p<0.001). No significant difference was observed between the Kaplan-Meier survival estimates of the two cohorts (p=0.54). After adjusting for patient characteristics including age, sex, co-morbidity index, race, receipt of chemotherapy, and tumor characteristics including tumor size, tumor grade, pathologic tumor stage, and pathologic nodal stage, adjuvant RT was not associated with improved OS in patients who underwent R0 resection (HR 1.01, 95% CI 0.63 - 1.60, p=0.98). However, tumor size >6cm (HR 1.54, 95% CI 1.03 - 2.32, p=0.04), high tumor grade (HR 3.46, 95% CI 1.83 - 6.55, p<0.001), and pathologic N1 stage (HR 2.30, 95% CI 1.06 - 4.94, p=0.03) were associated with worse OS in patients who underwent R0 resection. Conclusions: Treatment with adjuvant RT in patients with ACC who underwent R0 resection was not associated with an OS benefit. Further studies assessing optimal treatment for large and high-grade tumors with lymph node metastases are warranted. Presentation: Friday, June 16, 2023