A patient with a malignant extraadrenal retroperitoneal paraganglioma had elevated levels of immunoreactive neuropeptide Y (NPY) in the peripheral blood (5988 pg/ml; normal, 123 ± 30 pg/ml [mean ± standard error of the mean]). A 6‐month course of chemotherapy allowed surgical removal of the previously unresectable primary tumor. Postoperatively, the plasma NPY level initially fell to 1089 pg/ml; continued chemotherapy caused an additional decrease to 440 pg/ml. Four months after surgery, the plasma NPY level increased to 940 mg/ml, coincident with hepatic metastases. This case is the first report of a NPY‐secreting clinically nonfunctional malignant extraadrenal paraganglioma. Determination of circulating NPY levels may be useful in the diagnosis and follow‐up of patients with neuroendocrine tumors. Cancer 1992; 70:2350‐2353.
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