Figure 4 Immunohistochemical characterization of adrenal cortical adenoma. (A) Hematoxylin and eosin staining showing preserved adrenal architecture with cortical neoplastic proliferation. (B–K) Immunohistochemical staining profiles of the tumor tissue: (B) CD56 shows positive membranous staining, suggestive of neuroendocrine differentiation. (C–H) Negative immunoreactivity for chromogranin A, calcitonin, epithelial membrane antigen, glial fibrillary acidic protein, Ki-67 (low proliferative index), and S-100, respectively, supporting a benign cortical origin. (I) Vimentin shows diffuse cytoplasmic positivity, consistent with mesenchymal expression in adrenal cortical tumors. (J) α-Inhibin staining is negative, further excluding adrenal cortical carcinoma. (K) Synaptophysin is negative, ruling out medullary neoplasms. Together, these findings confirm the diagnosis of a benign adrenal cortical adenoma with focal medullary hyperplasia and exclude other cortical and medullary neoplasms.