The effect of weight change on changes in breast density measures over menopause in a breast cancer screening cohort

INTRODUCTION: High weight and high percentage mammographic breast density are both breast cancer risk factors but are negatively correlated. Therefore, we wanted to obtain more insight into this apparent paradox. METHODS: We investigated in a longitudinal study how weight change over menopause is related to changes in mammographic breast features. Five hundred ninety-one participants of the EPIC-NL cohort were divided into three groups according to their prospectively measured weight change over menopause: (1) weight loss (more than −3.0 %), (2) stable weight (between −3.0 % and +3.0 %), and (3) weight gain (more than 3.0 %). SPSS GLM univariate analysis was used to determine both the mean breast measure changes in, and the trend over, the weight change groups. RESULTS: Over a median period of 5 years, the mean changes in percent density in these groups were −5.0 % (95 % confidence interval (CI) −8.0; −2.1), −6.8 % (95 % CI −9.0; −4.5), and −10.2 % (95 % CI −12.5; −7.9), respectively (P-trend = 0.001). The mean changes in dense area were −16.7 cm(2) (95 % CI −20.1; −13.4), −16.4 cm(2) (95 % CI −18.9; −13.9), and −18.1 cm(2) (95 % CI −20.6; −15.5), respectively (P-trend = 0.437). Finally, the mean changes in nondense area were −6.1 cm(2) (95 % CI −11.9; −0.4), −0.6 cm(2) (95 % CI −4.9; 3.8), and 5.3 cm(2) (95 % CI 0.9; 9.8), respectively (P-trend < 0.001). CONCLUSIONS: Going through menopause is associated with a decrease in both percent density and dense area. Owing to an increase in the nondense tissue, the decrease in percent density is largest in women who gain weight. The decrease in dense area is not related to weight change. So the fact that both high percent density and high weight or weight gain are associated with high postmenopausal breast cancer risk can probably not be explained by an increase (or slower decrease) of dense area in women gaining weight compared with women losing weight or maintaining a stable weight. These results suggest that weight and dense area are presumably two independent postmenopausal breast cancer risk factors.