Insulin-like Growth Factor 1 Receptors in Human Breast Cancer and Their Relation to Estradiol and Progesterone Receptors¹

Insulin-like growth factor 1 (IGF1) binding sites were characterized in breast cancer. We demonstrate the presence of one high affinity binding site. Chemical cross-linking of ¹²⁵I-IGF1 to breast cancer membranes in reducing condition and sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed one band with an apparent molecular weight of 130,000. The specificity of the binding was studied. IGF2 was a good competitor whereas insulin competed with a potency lower than 1/100 that of IGF1. This IGF1 binding corresponded to the previously described type 1 IGF receptor (IGF1-R). IGF1-R was determined in 76 human breast cancer biopsies. Ninety-three % of the tumors were positive. The specific binding range was 0–16.4%; the geometric IGF1-R mean level was 3.9%. There was a relation (x² test) between IGF1-R and progesterone receptor positivity rates (P = 0.002). The IGF1-R concentrations were correlated (Spearman test) with those of estradiol receptor (P = 0.0018) and progesterone receptor (P = 0.0011). A positive linear correlation existed between IGF1-R and estradiol receptor (P = 0.006) and between IGF1-R and progesterone receptor (P = 0.003). Our demonstration of the presence of IGF1-R in human breast cancer biopsies suggests that IGF1, acting either via the endocrine, paracrine, or autocrine pathways, could stimulate tumor growth.