Abstract
Our study in the Nurses' Health Study (NHS) and NHS2, a nested case-control study with 1260 cases and 2221 controls, investigated the association between C-peptide levels, mammographic density (MD) parameters, V (a measure of gray scale variation), and breast cancer (BC) risk. We also examined how C-peptide and BC risk vary across quartiles of mammographic features. Linear and logistic regressions were used to study the associations between C-peptide and MD parameters, and breast cancer. C-peptide was inversely associated with percent MD and positively with non-dense area, but no associations were found with dense area and V measure. C-peptide was associated with an increased risk of invasive BC risk (top vs. bottom quartile, odds ratio = 1.46, 95% CI: 1.12-1.91). No multiplicative interactions were found between C-peptide, MD parameters, and BC risk. Our results suggest a positive association between C-peptide and BC risk, and MD parameters do not seem to modify this association.