Remarkably suppressed manganese superoxide dismutase activity in malignant pheochromocytoma.

There are almost no special histopathological characteristics or criteria that exactly define a malignant pheochromocytoma. Tissue concentrations of catecholamine metabolites and superoxide dismutase activity have been proposed as possible candidates for discriminating between benign and malignant pheochromocytomas. Tissue concentrations of dihydroxyphenylalanine, metanephrine, normetanephrine, vanillylmandelic acid, and 3-methoxy-4-hydroxyphenylethylglycol were determined in 29 normal adrenal medullas, 13 benign pheochromocytomas and 6 malignant pheochromocytomas, respectively. The copper-zinc superoxide dismutase and manganese superoxide dismutase activities in remnants of these tissues were determined by interruption of nitric formation from hydroxylamines. Catecholamine metabolites and copper-zinc superoxide dismutase activity in benign and malignant pheochromocytomas were identical. Manganese superoxide dismutase activity in malignant pheochromocytoma was the lowest among the groups examined. These data suggest that the assay of catecholamine metabolites in removed specimens is not a reliable method for making a differential diagnosis of benign or malignant pheochromocytoma. However, a low level of manganese superoxide dismutase activity in malignant pheochromocytoma may be a marker for malignancy of this neoplasm.