Malignant phaeochromocytoma with widespread metastasis in the rat.

Malignant phaeochromocytomas occurring in the adrenals of 2 aged male rats are reported. The primary tumour was unilateral and had metastasized to the other adrenal, pancreas, liver, spleen, lung, kidney and bone marrow. Metastatic deposits were also seen in a co-existing pituitary tumour and in an islet cell carcinoma of the pancreas. The cells, although resembling normal medullary cells, were smaller and had sparse cytoplasm; the nuclei were generally hyperchromatic. The cells were arranged in nests and sometimes in a trabecular pattern. The presence of phaeochromocytomas with widespread metastasis is of interest since, in general, phaeochromocytomas of rats are not prone to metastasize. In addition, invasion into a pancreatic islet cell tumour and into a pituitary tumour was unusual.