Insulin and Insulin-like Growth Factor and Risk of Postmenopausal Estrogen Receptor–Positive Breast Cancer: A Case–Cohort Analysis

Abstract

Background: Higher concentration of insulin-like growth factor-1 (IGF-1) increases postmenopausal breast cancer risk, but evidence for insulin and c-peptide is limited. Furthermore, not all studies have accounted for potential confounding by biomarkers from other biological pathways, and not all were restricted to estrogen receptor (ER)–positive breast cancer. Methods: This was a case–cohort study of 1,223 postmenopausal women (347 with ER-positive breast cancer) from the Melbourne Collaborative Cohort Study. We measured insulin, c-peptide, IGF-1, insulin-like growth factor binding protein-3, and biomarkers of inflammatory and sex-steroid hormone pathways. Poisson regression with a robust va..