Immunohistochemical estimations of growth activity to predict biological behavior of pheochromocytomas

To determine the usefulness of immunohistochemical estimations of growth activity to predict biological behavior of pheochromocytomas (PC), 42 cases of PC (33 adrenal and nine extra-adrenal tumors) were studied by immunohistochemistry using the monoclonal antibody, MIB-1. The mean MIB-1-positive cell rate for all 42 PCs was low (1.4%). The MIB-1-positive cell rates of adrenal PCs were significantly higher in malignant tumors (mean, 3.30%) than in benign tumors (mean, 0.81%) (P = .0184). In extra-adrenal PCs, the difference between benign (mean, 0.44%) and malignant (mean, 5.10%) tumors was also statistically significant (P = .0004). Other clinicopathologic factors, including family history, age, sex, and multiple endocrine neoplasm (MEN) type II status were also examined and were not statistically significant. In conclusion, estimation of the MIB-1-positive cell rate is useful for histologic distinction between benign and malignant pheochromocytomas. Especially, it is important to note that a high MIB-1-positive cell rate (>2%) is highly suggestive of malignancy.