Parameters reported to differentiate ACC from ACA in dogs are somewhat controversial and include peripheral fibrosis, capsular invasion, trabecular growth pattern, hemorrhage, necrosis, single-cell necrosis, hematopoiesis, fibrin thrombi, cytoplasmic vacuolation and increased proliferation index assessed by immunohistochemistry for the Ki67 antigen (2, 11, 12, 30). The gene discussed is MKI67; the disease is adrenal cortex carcinoma.