Population-based, case-control study of blood C-peptide level and breast cancer risk

Insulin resistance has been suggested to be associated with an increased ri sk of breast cancer. Insulin sensitivity can be measured using blood C-pept ide, a marker of insulin secretion. It is thus conceivable that blood C-pep tide levels may be associated with breast cancer risk. To evaluate this hyp othesis, we analyzed data from a subset (143 case-control pairs matched by age and status of menopause) of women who participated in the Shanghai Brea st Cancer Study, a population-based, case-control study conducted in Shangh ai during 1996-1998. Fasting blood samples were collected from study subjec ts to measure C-peptide levels. For cancer patients, the samples were colle cted before any cancer therapy. Conditional logistic regression was used to estimate adjusted odds ratios and 95% confidence intervals related to C-pe ptide levels. Breast cancer risk was increased with increasing levels of C- peptide (trend test, P = 0.01), with an odds ratio of 2.7 (95% confidence i nterval = 1.2-5.9) observed for the highest compared with the lowest tertil e of C-peptide concentration after adjusting for body mass index and age at the first live birth. The risk was not altered after fully adjusting for o ther traditional risk factors for breast cancer. This positive association was observed in both pre and postmenopausal women and regardless of the lev els of waist-to-hip ratio or body mass index. The results from this study w ere consistent with the insulin-resistance hypothesis for breast cancer and suggest that increased levels of C-peptide may contribute to the developme nt of breast cancer.