Ectopic secretion of neurohypophyseal peptides in patients with malignancy.

A great deal of information has been accumulated on the synthesis and release of AVP, oxytocin, and their associated neurophysins under normal circumstances. In 1957, Schwartz and Bartter first described SIAD in patients with lung cancer and postulated that the clinical findings were the results of excessive vasopressin secretion. Tumors have been known since 1964 to produce vasopressin, and small cell (oat cell) carcinoma of the lung is by far the most frequent malignant cause of SIAD. The biosynthetic pathway for the synthesis of AVP and its associated neurophysin (and to a lesser extent, oxytocin and its neurophysin) is well described and is similar if not identical to the synthesis of these peptides in the hypothalamus. However, there is little reliable information on the control of peptide synthesis and release by these tumors. The clinical picture of SIAD is well described and occurs in 20% to 40% of patients with SCCL, although up to 88% of patients with extensive SCCL have elevated circulating levels of one or more neurohypophyseal peptides. This information has led to considerable interest in the use of these peptides as tumor markers for the diagnosis, evaluation, and assessment of therapy in these patients. With the recognition of the high incidence of secretion of neurohypophyseal peptides by SCCL, studies have been initiated to determine the value of radioactive vasopressin neurophysin antibodies in localizing tumors that synthesize these peptides. The studies provide potentially useful information in diagnosing and following patients with SCCL and also offer some promise that radiolabeled antineurophysins could eventually be used to treat these patients.