Perimenopausal stage and breast density in US Chinese women Free

B41

Breast density is known to decrease with age, and previous studies comparing pre- and post-menopausal women also suggest that it decreases with menopause. Whether changes associated with menopause - but occurring before a woman is generally classified as postmenopausal - produce a decrease in density independently of increasing age is unknown. Objectives. We looked among a sample of pre- and peri-menopausal US Chinese women to determine if breast density varies by stage of perimenopause (pre-, early peri-, and late peri-menopause) independently of age. Methods. Between November, 2005, and October, 2007, we recruited 386 Chinese women in the Philadelphia region into a longitudinal study of diet, acculturation, and breast density. All women reported having menstruated within the past year. Baseline data collection included interviewer-administered questionnaires, anthropometry, and screening mammograms. Women were categorized into one of three perimenopausal stages (premenopausal (Pre), early perimenopausal (EPeri), or late perimenopausal (LPeri) based on their reported occurrence of menses during the previous year and its predictability during the previous three months. In preliminary analyses, breast density was assessed in 300 women from digitized cranial-caudal views using a computer-assisted method. We used multivariate linear regression to quantify associations between perimenopausal stage and breast density. Results. Among 290 women with complete covariate data, mean age was 44.5 ± 4.3 (range 35-56) y, and mean percent breast density was 47.1 ± 16.3%. Two-thirds (65%, N=188) of the women were classified as Pre, 25% (N=73) as EPeri, and 10% (N=29) as LPeri. We observed a significant decrease in percent density (Pre 49.8% vs. LPeri 36.6%, p<0.0001), a significant increase in non-dense tissue area (Pre 32.3 vs. LPeri 50.0 cm2, p=0.0006), and a non-significant decrease in dense tissue area (Pre 30.2 vs. LPeri 26.6 cm2, p=0.33) with advanced perimenopausal stage. Adjustment for age diminished differences for percent density (Pre 49.1% vs. LPeri 39.5%, p=0.007) and non-dense tissue area (Pre 33.7 vs. LPeri 43.8 cm2, p=0.08), but the effect of perimenopausal stage on percent density remained significant. Further adjustment for body mass index, waist circumference, and number of live births did not materially change results. Conclusion. Our cross-sectional data from a sample of pre- and peri-menopausal women suggest that changes occurring early during the menopausal transition result in a decrease in breast density independently of age. Additional longitudinal studies are required to clarify the hormonal mechanisms related to aging and to menopause that, whether separately or cooperatively, reduce breast density.