Abstract 593: Mammographic breast density in postmenopausal women is affected by the age of first full term pregnancy
Authors: Vandeloo Magda J. , Neven Kristof Y. , Bruckers Liesbeth , Russo Jose , Vancoullie Liesbeth , Bijnens Esmée , Kellen Eliane , Nawrot Tim S. , Ongeval Chantal Van 
Published: August 2019

Abstract
Mammographic breast density (MBD) is accepted as a risk factor in breast cancer, whereas age of first full term pregnancy (FFTP) has been demonstrated to be a protective one. The objective of this study is to investigate the association between reproductive history and MBD at menopause. Women, age 50-69y, participating in the Flemish (Belgium) governmental organised breast cancer screening program were invited to participate in the study during their visit at the mammography department in Leuven (hospital and the mobile unit). The study was approved by the ethical committee of the hospital. After signing the informed consent, a self-administered questionnaire (SAQ) providing information on lifestyle and environmental exposure was completed by the participants. In the present work we present the analysis of the first 640 women that completed the SAQ and underwent mammography. Questionnaire data were registered via the Qualtrics software. The three parameters of MBD (VolparaDataManager®, USA) included the percentage glandular tissue of the total breast volume (GLAND), the ratio of the glandular tissue volume compared to the whole breast volume or Volumetric Breast Density (VBD) and the BIRADS density classification. We applied linear regression models to investigate the association between the continuous breast density markers (GLAND and VBD, log transformed) and the following explanatory variables: age of woman, ever pregnant, number of pregnancies, age of FFTP, ever breastfed (BF), amount and duration of BF, and breastfeeding in FFTP. An ordinal logistic regression model was used for the breast density marker BIRADS. The average GLAND and VBD changes with a multiplicative factor of 1.073 (p = 0.013) and 1.072 (p = 0.013) for a 5-year increase of age of FFTP. Thus, an increase of 5 years in age of FFTP is associated with about 7% increase in geometric mean of GLAND and VBD. The odds ratio for a higher versus a lower score of the BIRADS classification is 1.24 (p = 0.023) greater for every 5-year increase in age of FFTP. These results are independent for the inverse association between the age of the woman and the MBD markers. For a 5 year increment in age, geometric GLAND (p = 0.019) and VBD (p = 0.024) are approximately 5% lower and the odds ratio for a higher BIRADS score is 12% higher (p = 0.079). There is no association between the MBD markers and breastfeeding, the number and duration BF, and the number of pregnancies after correcting for age and age of FFTP. In conclusion, this study is to our knowledge the first one to show that MBD is significantly reduced when pregnancy takes place at early age.( This study was supported by a Grant of the Breast Cancer Organization Think Pink of Belgium, the Department of Breast Radiology and Mobile Unit of the University Hospital Leuven, the Center of Environmental Sciences and the Center of Biostatistics of the Hasselt University, and NIH Grant CA06927 to FCCC, PA, USA.)
Citation Format: Magda J. Vandeloo, Kristof Y. Neven, Liesbeth Bruckers, Jose Russo, Liesbeth Vancoullie, Esmée Bijnens, Eliane Kellen, Tim S. Nawrot, Chantal Van Ongeval. Mammographic breast density in postmenopausal women is affected by the age of first full term pregnancy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 593.