Somatostatin receptors are present in small-cell but not in non-small-cell primary lung carcinomas: relationship to EGF-receptors.

Sixteen primary human lung tumours were analysed for their content of somatostatin receptors using receptor autoradiography with somatostatin-28 and somatostatin octapeptide analogues as radio-ligands. Two out of 4 small-cell lung carcinomas were somatostatin receptor-positive, with a high density of homogeneously distributed receptors on tumour tissue only. Somatostatin receptors were characterized in one of the tumours in homogenate binding assay as saturable, high-affinity binding sites (KD = 0.53 nM) with a number of sites (Bmax) equivalent to 189 fmoles/mg protein. These sites were specific for somatostatin, since only biologically active somatostatin analogues but not unrelated peptides showed high-affinity binding. Both receptor-positive patients had limited disease; furthermore, the small-cell lung carcinoma patient with the longest survival was receptor-positive, while the one with the shortest survival was receptor-negative. None of the 12 non-small-cell lung carcinomas (5 squamous carcinomas, 7 adenocarcinomas) contained somatostatin receptors. For comparison, epidermal growth factor receptors were found in all non-small-cell lung carcinomas. Neuroendocrine features (synaptophysin, chromogranin, neuron-specific enolase, protein gene product 9.5) were present in all small-cell lung carcinomas but absent in non-small-cell lung carcinomas. Given the receptor-mediated action of somatostatin in other neuroendocrine tumours, these data may have a bearing on the clinical application of somatostatin analogues in patients with small-cell lung carcinomas.