Mammographic density in birth cohorts of Danish women: a longitudinal study

Abstract

BackgroundBreast cancer is the leading malignant disease among western women with incidence increasing over time. High mammographic density is a well-established risk factor for breast cancer. We explored trends in mammographic density across birth cohorts to gain further insight into possible time trends in women’s mammographic density that might explain the historical increase in breast cancer incidence.MethodsData derived from two mammography screening programs in Denmark from 1991 to 2001, including on average 41,091 women from Copenhagen and 52,938 women from Funen aged 50–69. Mammographic density was assessed qualitatively (fatty or mixed/dense) by senior screening radiologists. The proportion of women with mixed/dense mammographic density was calculated by age at screening, screening period, and birth cohort. The Generalized Estimating Equations were used to calculate odds ratios and 95% confidence intervals. All statistical tests were two-sided.ResultsThe proportion of women with mixed/dense mammographic density increased from 45% among women born in the 1920s to 75-80% among women born in the 1940s. In Copenhagen, the age-adjusted odds ratio (95% CI) of mixed/dense mammographic density in women born in 1941–42 was 2.48 (2.22-2.76) compared with women born in 1921–22. In Funen, the age-adjusted odds ratio of mixed/dense mammographic density in women born in 1946–47 was 5.89 (5.32-6.51) compared with women born in 1924–25. Hormone use had a greater impact on mammographic density in birth cohorts of the 1920s compared with those of the 1940s.ConclusionsWe found suggestive evidence of a birth cohort pattern in mammographic density and an attenuated impact of hormone use in younger compared with older birth cohorts suggesting that postmenopausal mammographic density could be linked to changing exposures accumulated over time in women’s lives.

Birth weight, childhood body mass index, and height in relation to mammographic density and breast cancer: a register-based cohort study

“…We detected a strong effect of birth cohort on MD, finding that younger cohorts of women (born in 1945 to 49) had significantly higher MD than women from the oldest cohorts (1930 to 1934), in agreement with Hellman et al . [43]. Our study expands on evidence provided by Harris et al .…”

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

“…Users of hormone therapy have a higher mammographic density than nonusers . The possible birth cohort effect on mammographic density observed in the earlier Danish study was seen for both users and nonusers of hormone therapy, but the density levels were considerably higher in the user than in the nonuser group . The Dutch data analyzed in our study were derived from September 2003 to September 2016.…”

“…In a recent pooled analysis, the effect of aging and menopausal status on mammographic density was investigated, and the authors found density to decrease with increasing age, and to be lower in postmenopausal than in premenopausal women of the same age. A Danish study with repeated measurements for the same women over a 10‐year period indicated a birth cohort effect on density with an increase in the proportion of women with mixed/dense mammographic density from women born in the 1920s to women born in the 1940s.…”

Comparison of Danish dichotomous and BI-RADS classifications of mammographic density

“…During the early screening period from 1991–2001, one- or two-view mammograms were taken and mammographic density assessed by highly trained radiologists. Mammographic density refers to the regions of non-radiolucent, or bright, portions of the radiographic image of the breast, and represents the relative proportion of fibroglandular to fatty tissue ( 4 – 7 ).…”

“…High mammographic density is one of the strongest known risk factors for breast cancer ( 7 , 8 ), associated with a four- to six-fold increased risk of breast cancer when comparing women with high density in more than 75% of the breast to those with less than 5% mammographic density ( 4 ). Additional risk factors for breast cancer include the female gender, genetic inheritance, age, country of birth, parity, body mass index (BMI), age at onset of menarche and menopause, and hormone replacement therapy (HRT) ( 5 , 9 , 10 ).…”