Immunohistochemical evaluation of apelin and VEGF expression in cortisol-producing adrenal adenomas

PURPOSE: In this study, we aimed to investigate the immunohistochemical expression of apelin in tissue samples obtained from patients with Cushing's syndrome (CS) due to cortisol-producing adrenal adenoma (CPA) and to compare these findings with normal adrenal cortex tissue. Additionally, we sought to evaluate the association of apelin expression with clinical, hormonal, and histopathological parameters. The expression profile of vascular endothelial growth factor (VEGF) was also assessed to explore potential angiogenic interactions. METHODS: This retrospective, single-center study included 11 patients diagnosed with CPA and 15 control subjects with histologically normal adrenal cortex tissue. Formalin-fixed, paraffin-embedded tissue sections were subjected to immunohistochemical staining for apelin and VEGF. Immunohistochemical evaluation was performed by assessing staining intensity and the percentage of positively stained cells. An immunoreactivity score (IRS) was calculated by combining these parameters to provide a semi-quantitative measure of protein expression. RESULTS: Apelin staining intensity was significantly higher in CPA tissues compared with controls (p = 0.026), whereas the percentage of apelin-positive cells and IRS values did not differ significantly between groups. In an exploratory ROC analysis, apelin staining intensity showed moderate discrimination between CPA and control adrenal cortex tissues (AUC = 0.776, 95% CI: 0.581-0.971, p = 0.018). In bias-reduced univariable logistic regression, apelin staining intensity was associated with CPA (OR = 2.96, 95% CI: 1.02-8.60, p = 0.046), although the wide confidence interval indicated considerable uncertainty. VEGF staining parameters did not differ significantly between CPA and control tissues. No statistically significant correlations could be demonstrated between apelin or VEGF IRS and the evaluated clinicopathological or hormonal parameters. CONCLUSION: Apelin staining intensity was higher in CPA than in normal adrenal cortex, whereas the proportion of apelin-positive cells and IRS did not differ significantly between groups. VEGF staining parameters also did not differ significantly between CPA and control tissues. These findings suggest altered apelin immunoreactivity in CPA; however, given the exploratory nature and small sample size of the study, larger studies are required to confirm these observations and clarify their biological significance. CLINICAL TRIAL NUMBER: Not applicable.