Premenopausal insulin-like growth factor-I serum levels and changes in breast density over menopause.

BACKGROUND A high proportion of glandular and stromal tissue in the breast (percentage breast density) is a strong risk factor for breast cancer development. Insulin-like growth factor-I (IGF-I) is hypothesized to influence breast cancer risk by increasing breast density. OBJECTIVES We studied the relation between premenopausal circulating IGF-I levels and premenopausal and postmenopausal, absolute nondense and dense area, and percentage breast density as well as changes in these measures over menopause. DESIGN AND METHODS Mammograms and blood samples of 684 premenopausal participants of the Prospect-European Prospective Investigation into Cancer and Nutrition cohort were collected at baseline. A second mammogram of these women was collected after they became postmenopausal. Premenopausal IGF-I levels were measured in serum. Premenopausal and postmenopausal breast measures were assessed using a computer-assisted method. Mean values of breast measures were calculated for quartiles of serum IGF-I using linear regression analysis. RESULTS Women with higher premenopausal IGF-I levels showed a slightly smaller decrease in dense area over menopause (-12.2 cm2 in the highest versus -12.9 cm2 in the lowest quartile; P trend = 0.58) and, at the same time, a smaller increase in the nondense (fat) area (P trend = 0.09). Due to the changes over menopause, high premenopausal IGF-I serum levels were associated with lower nondense area (P trend = 0.05), somewhat higher dense area (P trend = 0.66), and consequently higher percentage breast density (P trend = 0.02) after menopause. CONCLUSION AND DISCUSSION Women with higher premenopausal IGF-I levels have a smaller increase in nondense area and also a slightly smaller decrease in absolute dense area during menopause, resulting in higher breast density after menopause.