Increased plasma motilin concentrations in small cell carcinoma of the lung

Plasma samples from 21 patients with small cell carcinoma of the lung were screened for pancreatic polypeptide, somatostatin, motilin, and vasoactive intestinal polypeptide. One patient had severe impairment of both renal and liver function. In the 20 remaining subjects vasoactive intestinal polypeptide concentrations were normal, and only two patients had increased concentrations of somatostatin. Increases in pancreatic polypeptide were detected more commonly (7/20), but these may have been non-specific age related increases. The major finding was high concentrations of motilin (greater than 496 pg/ml) in 17 of 20 patients. Plasma motilin was subsequently assayed in 16 more patients with lung cancer, including 10 patients with non-small cell carcinoma of the lung. At concentrations over 900 pg/ml plasma motilin appears to be a tumour marker for small cell carcinoma of the lung with acceptable sensitivity (59%) and specificity (78%). The origin of increased plasma motilin in small cell carcinoma of the lung was investigated. Bombesin (gastrin releasing peptide), a peptide known to stimulate the release of motilin in man, was, as in previous studies, detected in tumour but not in plasma, except in one patient out of 21. Immunohistochemical studies failed to detect motilin antigen in biopsy samples. Motilin tumour content was found to be low in tumour tissue from three patients with small cell carcinoma of the lung who had appreciable hypermotilinaemia and from three patients with non-small cell carcinoma of the lung who had either normal or slightly raised plasma motilin concentrations. The stimulus to motilin secretion in patients with small cell carcinoma of the lung remains unclear.