IGF1 and breast cancer: Early life body fatness could also influence breast density and cancer risk through altered levels of insulin-like growth factor-1 (IGF-1): increased weight during childhood is directly associated with IGF-1 measured concurrently [46, 47] but early life body size was inversely correlated with IGF-1 levels measured later in adulthood in the Nurses’ Health Study [48], suggesting a possible pathway linking childhood/adolescent body fatness, mammographic density, and breast cancer risk.