Somatostatin secretion by lung and thymic tumours.

Ectopic secretion of somatostatin in one patient with a thymic tumour and in two patients with lung tumours is described. All three patients also had ectopic ACTH secretion. Gel filtration chromatography under dissociating conditions showed the two lung tumour extracts to contain predominantly 1600 MW somatostatin monomer while the thymic tumour contained predominantly a 3000-3500 MW form of somatostatin, 77% of which was not converted to 1600 MW somatostatin by dithiothreitol (an agent which reduces disulphide bridges). This form may therefore represent a covalently-bound precursor of somatostatin rather than a dimer of two somatostatin monomers. Plasma from all three tumour patients and from normal subjects contained both 1600 and 3000--3500 MW somatostatin. It is suggested that somatostatin secretion may frequently be associated with multiple hormone producing tumours.