Immunohistochemical estimations of growth activity to predict biological behavior of pheochromocytomas

To determine the usefulness of immunohistochemical estimations of growth ac tivity to predict biological behavior of pheochromocytomas (PC), 42 cases o f PC (33 adrenal and nine extra-adrenal tumors) were studied by immunohisto chemistry using the monoclonal antibody, MIB-1, The mean MIB-1-positive cel l rate for all 42 PCs was low (1.4%). The MIB-1-positive cell rates of adre nal PCs were significantly higher in malignant tumors (mean, 3.30%) than in benign tumors (mean, 0.81%) (P = .0184), In extra-adrenal PCs, the differe nce between benign (mean, 0.44%) and malignant (mean, 5.10%) tumors was als o statistically significant (P = .0004). Other clinicopathologic factors, i ncluding family history, age, sex, and multiple endocrine neoplasm (MEN) ty pe II status were also examined and were not statistically significant. In conclusion, estimation of the MIB-1-positive cell rate is useful for histol ogic distinction between benign and malignant pheochromocytomas, Especially , it is important to note that a high MIB-1-positive cell rate (>2%) is hig hly suggestive of malignancy.