Calcitonin gene-related peptide in small cell lung carcinomas

Calcitonin gene-related peptide (CGRP) is a regulatory peptide encoded by the calcitonin gene. CGRP is expressed in increased amounts by the cells of medullary thyroid carcinomas and has been demonstrated by immunohistochemistry to occur in neuroendocrine cells and nerve fibres of lung tissue.

Serum CGRP levels were measured in patients with small cell lung carcinomas before treatment (n = 74) and immediately before the second course of chemotherapy (n = 30). In-situ hybridization and immunohistochemistry were performed on tumour tissue and CGRP was extracted from two tumours and characterized by gel chromatography and high pressure liquid chromatography.

Serum CGRP levels were elevated in small cell lung carcinomas when compared with healthy controls of similar age and sex (median values 55.0 vs 36.6 pmol/l, P < 0.001), and 27% had levels above the upper normal range. Serum CGRP levels decreased following the initial course of chemotherapy (P < 0.05) but remained elevated when compared to the controls (P < 0.001). In-situ hybridization for CGRP mRNA was positive in three of 17 tumours and immunohistochemistry was positive in seven of 31 tumours investigated. CGRP immunoreactivity extracted from two tumours was characterized by gel chromatography and high pressure liquid chromatography. A major part of the immunoreactivity was demonstrated to represent the intact molecule.

We found that patients with small cell lung carcinomas had elevated concentration of serum calcitonin gene-related peptide but only 27% had values above the upper normal range. Serum CGRP is therefore of limited value as a tumour marker. Intact CGRP can be extracted from tumour tissue, but in-situ hybridization and immunohistochemistry showed positive reactions in only a few of the tumours investigated. The elevated serum CGRP levels are therefore likely to be largely of extratumoral origin.