Expression of insulin-like growth factor mitogenic signals in adult soft-tissue sarcomas: significant correlation with malignant potential

The insulin-like growth factor (IGF) signal transduction system involves receptors, ligands and binding proteins (IGFBPs) that have been shown to have mitogenic and distinct anti-apoptotic effects on malignant cell lines of both epithelial and mesenchymal origin. Expression of the IGF signal system might be a mechanism by which human soft-tissue sarcomas (STS) obtain a proliferative advantage over normal adjacent tissues. IGFBP2, one of at least six different binding proteins identified to date, is secreted by most sarcoma cell lines and appears to be involved in cell proliferation and transformation. Circulating levels of this protein are markedly increased in malignancy. We have assessed 46 adult STS specimens of low, intermediate and high pathological grade of malignancy for the immunohistochemical expression of IGFBP2, IGF1, IGF2, IGF1 receptor-α and -β (IGF1Rα/β). The protein expression was measured by quantitative color video image analysis and semi-quantitative evaluation, and the measurements correlated well (Spearman, P<0.001). Using both methods, significant differences in expression of IGFBP2 among each of the three grades, expression of IGF2 between intermediate and high grade, and expression of IGF1Rβ between low-intermediate and low-high grade were observed (Dunnett test, P<0.05). Multiple regression analysis for both quantitative and semi-quantitative data confirmed the significance of the relationship and independence of the proteins, except IGF2. We concluded that IGFBP2 and IGF1Rβ are independent predictors of the malignant potential of adult STS.