Expression of estrogen receptors in non-malignant mammary tissue modifies the association between insulin-like growth factor 1 and breast cancer risk.

BACKGROUND

Several studies have reported that the insulin-like growth factor 1 (IGF-1) is positively associated with estrogen receptor-positive [ER(+)] breast cancer risk, whereas there is little or no association with respect to ER(-) breast cancer. All comparisons of ER(+) breast cancer cases, however, have been made versus healthy controls, for whom there is no information about the ER expression in their mammary gland.

PATIENTS AND METHODS

In the context of a case-control investigation conducted in Athens, Greece, we studied 102 women with incident ERα(+) breast cancer and compared their IGF-1 blood levels with those of 178 ERα(+) and 83 ERα(-) women with benign breast disease (BBD) who underwent biopsies in the context of their standard medical care. Data were analysed using multiple logistic regression and controlling for potential confounding variables.

RESULTS

ERα(+) breast cancer patients had higher IGF-1 levels compared with women with BBD [odds ratio (OR) 1.36, 95% confidence interval (CI): 0.95-1.94, per 1 standard deviation (SD) increase in IGF-1 levels]. When ERα status of women with BBD was taken into account, the difference in IGF-1 levels between ERα(+) breast cancer patients and women with BBD was clearly driven by the comparison with BBD women who were ERα(+) (OR = 1.95, 95% CI: 1.31-2.89 per 1 SD increase in IGF-1 levels), whereas there was essentially no association with IGF-1 levels when ERα(+) breast cancer patients were compared with ERα(-) BBD women. These contrasts were particularly evident among post/peri-menopausal women.

CONCLUSIONS

We found evidence in support of an interaction of IGF-1 with the expression of ERα in the non-malignant mammary tissue in the context of breast cancer pathogenesis. This is in line with previous evidence suggesting that IGF-1 increases the risk of ER(+) breast cancer.