Expression of messenger RNA for insulin-like growth factors and insulin-like growth factor binding proteins by experimental breast cancer and normal breast tissue in vivo

We report the expression of insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) by breast cancer cells and normal breast tissue in vivo. N-nitrosomethyl-urea (NMU)-induced rat mammary tumors synthesize mRNAs for IGF-II and IGFBP-2, -3, and -4. In contrast, normal lactating breast contains only IGFBP-2 and IGF-II messages; IGFBP-3 and -4 mRNAs are absent in this tissue. IGF-I and IGFBP-1 mRNAs are not expressed in either NMU tumors or in normal breast. This is the first report of in vivo expression of IGFBPs and IGF-II messages in breast tumors.