IGF1 and obesity due to melanocortin 4 receptor deficiency: For example, strong positive associations between fasting insulin levels and postmenopausal breast cancer have been observed (67, 68) and found to largely explain the relationship of obesity with breast cancer (e.g., statistical adjustment for insulin but not sex hormones in multivariate models eliminated the relation of obesity with disease) (67, 69), whereas there are conflicting data regarding the association of circulating IGF-I and postmenopausal breast cancer (67, 70, 71).