The percentage of CD34 staining area was significantly lower in ACC (4.023 ± 0.408%) when compared to both adrenocortical adenoma with Cushing syndrome (ACAc) (9.947 ± 1.431%, p < 0.01) and non-functioning adrenocortical adenoma (ACAn) (7.988 ± 1.188%, p < 0.001). This evidence concerns the gene CD34 and Cushing syndrome.