Change in mammographic density across birth cohorts of Dutch breast cancer screening participants

High mammographic density is a well‐known risk factor for breast cancer. This study aimed to search for a possible birth cohort effect on mammographic density, which might contribute to explain the increasing breast cancer incidence. We separately analysed left and right breast density of Dutch women from a 13‐year period (2003‐2016) in the breast cancer screening programme.

First, we analysed age‐specific changes in average percent dense volume (PDV) across birth cohorts. A linear regression analysis (PDV vs. year of birth) indicated a small but statistically significant increase in women of: 1) age 50 and born from 1952 to 1966 (left, slope = 0.04, p =0.003; right, slope = 0.09, p<0.0001); 2) age 55 and born from 1948 to 1961 (right, slope = 0.04, p=0.01); and 3) age 70 and born from 1933 to 1946 (right, slope = 0.05, p=0.002). A decrease of total breast volume seemed to explain the increase in PDV.

Second, we compared proportion of women with dense breast in women born in 1946‐1953 and 1959‐1966, and observed a statistical significant increase of proportion of highly dense breast in later born women, in the 51 to 55 age‐groups for the left breast (around a 20% increase in each age‐group), and in the 50 to 56 age‐groups for the right breast (increase ranging from 27% to 48%).

The study indicated a slight increase in mammography density across birth cohorts, most pronounced for women in their early 50s, and more marked for the right than for the left breast.

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