Improvement in Recurrence-free Survival with Adjuvant Radiation in Adrenocortical Carcinoma

Abstract

Adrenocortical carcinoma (ACC) is a rare malignancy with high rates of local recurrence and poor prognosis. Given high propensity to metastasize, the role of post-operative radiation therapy (RT) in localized ACC has been controversial. We sought to evaluate the benefit of adjuvant RT to local control in our updated institutional ACC database. From 424 patients in our ACC database, we retrospectively identified patients who underwent adjuvant RT at our institution from 1999 to 2017. Patients that were treated with surgery followed by adjuvant RT were matched to patients who only underwent resection on the basis of stage, surgical margin status, tumor grade, and adjuvant mitotane use. Local recurrence was defined as adrenal bed or abdominal failure. Overall and recurrence-free survival probabilities were estimated using the Kaplan-Meier method. Distributions were compared between cases and controls using the log-rank test statistic. Cox proportional hazards regression models were used to estimate the hazard ratio for time-to-event endpoints comparing controls to cases after adjustment for age at event and gender. Of 424 patients, 78 patients with ACC were selected, half who underwent adjuvant radiation. Patients were matched 1:1 without significant differences with respect to stage, margin status, grade, or mitotane use, although there were more females than males in the matched group (52.8% females with RT, 82% without RT). Median radiation dose was 55 Gy (range 45-60 Gy). Local recurrence was less common with adjuvant RT (13 vs 26 local failures in those treated with and without RT, respectively, (p = 0.038, hazard ratio [HR] 2.20; 95% confidence interval [CI] 1.04-4.63)). Five-year recurrence-free survival for patients with RT was 46.7% and 16.9% for patients without (p = 0.016; HR 2.32, 95% CI 1.14-4.57). There was numerically better overall survival in patients that received RT (72.1% versus 55.1%), although this was not statistically significant (p = 0.424, HR 1.46, 95% CI 0.58-3.68). Adjuvant RT following gross resection of ACC significantly improves recurrence free-survival in this retrospective case-matched cohort analysis. Even though, this represents the largest series to date on adjuvant RT for ACC, prospective confirmation of this data is needed.