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. 2025 Feb 1;5(2):267-276.
doi: 10.1158/2767-9764.CRC-24-0561.

Age at First Full-term Pregnancy and Other Reproductive Factors Are Associated with Mammographic Breast Density in Postmenopausal Women: A Study in Flanders, Belgium

Magda J Vandeloo  1   2   3 , Eliane Kellen  4   5 , Carolyn Y Fang  3 , Eric A Ross  6 , Liesbeth Vancoillie  7 , Liesbeth M Bruckers  8 , Kristof Y Neven  2 , Esmée M Bijnens  2   9 , Tim S Nawrot  2   10 , Chantal Van Ongeval  1   7
Affiliations

Age at First Full-term Pregnancy and Other Reproductive Factors Are Associated with Mammographic Breast Density in Postmenopausal Women: A Study in Flanders, Belgium

Magda J Vandeloo et al. Cancer Res Commun. .

Abstract

Abstract: This study evaluated the association between age at first full-term pregnancy (FFTP) and mammographic breast density (MBD) in postmenopausal women. A total of 1,034 women, ages 50 to 69 years, were recruited from the Flemish (Belgium) population–based breast cancer screening program. Participants completed a questionnaire on lifestyle and reproductive factors. From mammography, we assessed the percentage glandular tissue of the total breast volume (GLAND), the volumetric breast density (VBD), and the Breast Imaging Reporting and Data System (BI-RADS) density classification. For statistical analysis, we used the piecewise linear regression model. The average age at FFTP was 26.1 years. Among women with an FFTP > 25.7 years, an each year increase in FFTP age was associated with a 1.17% increase in GLAND [95% confidence interval (CI), 0.20%–2.46%; P = 0.041] and a 1.45% increase in VBD (95% CI, 0.18%–2.75%; P = 0.026). Similarly, the odds of a higher BI-RADS classification increased by 5.0% (95% CI, 0.0%–11.0%; P = 0.059) for each year increase in FFTP age after 25.7 years. For every year delay in age at menarche, a 2.48% higher GLAND (95% CI, 0.43%–4.57%; P = 0.017) and a 2.45% higher VBD (95% CI, 0.38%–4.56%; P ≤ 0.020) were observed. Ever use of oral contraceptive resulted in a 12.24% decrease in GLAND (95% CI, −20.90% to −2.63%; P = 0.014) and a 13.48% decrease in VBD (95% CI, −22.1% to −3.91%; P = 0.007). MBD is significantly higher when FFTP takes place after 25.7 years. Later age at menarche is associated with higher MBD, whereas ever use of oral contraceptive is associated with lower MBD at postmenopause.

Significance: We consider our findings to be highly novel, and to the best of our knowledge, our study is one of the first to investigate associations between age at FFTP and three markers of MBD (GLAND, VBD, and BI-RADS), uncovering that MBD is significantly higher when FFTP occurs after 25.7 years.

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Conflict of interest statement

M.J. Vandeloo reports grants from the breast cancer organization “Think Pink” of Belgium and Fox Chase Cancer Center, Philadelphia, USA, during the conduct of the study. E.A. Ross reports grants from NCI during the conduct of the study, as well as grants from NCI outside the submitted work. No disclosures were reported by the other authors.

Figures

Figure 1
Figure 1
Selection process indicating the number of women recruited and excluded during the process of collection and data analysis.
Figure 2
Figure 2
Correlation between MBD and age at FFTP. Plots (A and B) show the association of the VBD [in ln (%)] and GLAND [in ln (cm³)] with age at FFTP (in years). Breakpoint is indicated as a red dotted line at 25.7 years.
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