Clinical Impact of Pathological Features Including the Ki-67 Labeling Index on Diagnosis and Prognosis of Adult and Pediatric Adrenocortical Tumors

Adrenocortical tumors (ACT) in the adult and pediatric population are generally considered distinct entities due to differences in molecular events related to tumorigenesis, clinical presentation, and outcome. Furthermore, pathological criteria used for diagnosis and prognostication of ACT in adults are usually inadequate for predicting the biological behavior of ACT in children. Here, we analyzed 146 adult and 44 pediatric (< 15y/o) ACT with long-term clinical follow-up and furthered current evidence on the clinical and pathological differences between pediatric and adult tumors. Predilection for female over male gender was observed in both cohorts, but more so in adults (84% vs. 61%, p = 0.003). Cushing syndrome was more frequent in adults (p < 0.001), whereas virilization, either isolated (p < 0.001) or combined to Cushing (p = 0.047), was more common in children. The Ki67 labelling index (LI) of pediatric adenomas and carcinomas was much higher than their corresponding tumors in adults (p < 0.001). Despite these differences, pathological analyses including the evaluation of Ki67 greatly improved patient prognostication in both age cohorts. Indeed, increased Weiss scores and Ki67 indexes correlated with poor overall- and disease-free survival in adult patients with carcinoma. Among the proliferative indexes tested, Ki67 LI ≥ 10% showed the highest hazard ratio (HR) for recurrence and the Ki67 LI ≥ 3% showed the highest HR for survival. In pediatric tumors, the Wieneke score (p < 0.001) and the Ki67 LI (p < 0.001) showed high accuracy for predicting biological behavior, and increased scores/indexes correlated with worse overall and disease-free survival. In this age cohort, Ki67 LI < 10% was able to rule out malignant behavior, whereas Ki67 LI ≥ 15% may be used to predict the patients with higher risks of recurrence and/or poor outcome.