Nested case-control study of the association of circulating levels of serum insulin-like growth factor I and insulin-like growth factor binding protein 3 with breast cancer in young women in Norway.

BACKGROUND

High circulating levels of insulin-like growth factor (IGF-I) may elevate the risk of breast cancer in premenopausal women, possibly by increasing cell proliferation and reducing apoptosis.

METHODS

We conducted a nested case-control study among 35,105 Norwegian women who participated in a health screening survey, ages 40 to 42 years, and who were subsequently followed for a mean period of 4.3 years. During this period, 325 women were diagnosed with breast cancer; 647 women without breast cancer, matched on age and time of blood sampling, were selected as controls. Serum concentrations of IGF-I and its main binding protein (IGFBP-3) were measured with radioimmunoassay, and logistic regression analysis was used to adjust for relevant covariates.

RESULTS

The mean age at blood collection was 41.1 years in both groups, and the mean age at diagnosis for the cases was 45.4 years (range, 40-51 years). The median IGF-I level did not differ between cases (205 ng/mL) and controls (202 ng/mL). When analyzed by categories of serum IGF-I, the relative risk for women in the highest versus the lowest quintile was 1.46 (95% confidence interval, 0.93-2.32; P(trend) = 0.15) after adjusting for serum IGFBP-3, age, and year of blood collection. The exclusion of cases that were diagnosed within 2 years after blood collection did not materially affect the results.

CONCLUSION

We found only a modest positive association between serum IGF-I levels and risk of breast cancer in women younger than 50 years of age.