Evidence for an increased somatomedin-C/insulin-like growth factor I content in primary human lung tumors

Immunoreactive somatomedin-C/insulin-like growth factor I (SM-C/IGF I) content was measured in human neoplastic lung tissue obtained from surgery on 10 patients (seven epidermoid carcinoma, three adenocarcinoma), and in normal lung tissue obtained from the same excised portion. SM-C/IGF I content in lung tumors was 615 +/- 123 (SE) milliunits/g of tissue (range, 214-1531), significantly higher (P less than 0.01) than normal tissue (234 +/- 51 milliunits/g of tissue; range, 37-537); in particular, every subject showed a clear-cut difference of SM-C/IGF I content between neoplastic and normal tissue (ratio, 3.41 +/- 0.69; range, 1.4-7.2). The results were essentially unchanged when data were expressed relative to hemoglobin or DNA tissue content. By contrast, in peripheral plasma SM-C/IGF I concentration was 0.51 +/- 0.17 units/ml, significantly lower (P less than 0.01) than in 59- to 70-yr-old control subjects (1.10 +/- 0.13 units/ml). In conclusion, the lung tumors studied, irrespective of their histological structure, contain more SM-C/IGF I than does normal tissue. Whether this is due to a primary in situ production of SM-C/IGF I or is secondary to overproduction of other inducers such as platelet derived growth factor-like peptides is yet to be clarified. The reduced circulating SM-C/IGF I concentration seems to be related more to the nutritional status of the patients.