title: Mammographic density and risk of breast cancer by adiposity: an analysis of four case-control studies.
abstract: The association of mammographic breast density with breast cancer risk may vary by adiposity. To examine effect modification by body mass index (BMI), the authors standardized mammographic density data from four case-control studies (1994-2002) conducted in California, Hawaii and Minnesota and Gifu, Japan. The 1,699 cases and 2,422 controls included 45% Caucasians, 40% Asians and 9% African-Americans. Using ethnic-specific BMI cut points, 34% were classified as overweight and 19% as obese. A single reader assessed density from mammographic images using a computer-assisted method. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI) while adjusting for potential confounders. Modest heterogeneity in the relation between percent density and breast cancer risk across studies was observed (p(heterogeneity)  = 0.08). Cases had a greater age-adjusted mean percent density than controls: 31.7% versus 28.5%, respectively (p <0.001). Relative to <20 percent density, the ORs for >35 were similar across BMI groups whereas the OR for 20-35 was slightly higher in overweight (OR = 1.69, 95% CI: 1.28, 2.24) and obese (OR = 1.62, 95% CI: 1.12, 2.33) than in normal weight women (OR = 1.49, 95% CI: 1.11, 2.01). Furthermore, limited evidence of effect modification by BMI of the OR per 10% increase in percent density (p(interaction)  = 0.06) was observed, including subgroup analyses by menopausal status and in analyses that excluded women at the extremes of the BMI scale. Our findings indicate little, if any, modification by BMI of the effects of breast density on breast cancer risk.
authors.affiliation: University of Hawaii Cancer Center, Cancer Epidemiology Program, Honolulu, HI, USA. sconroy@cc.hawaii.edu
authors.forename: Shannon M
authors.initials: SM
authors.lastname: Conroy
authors.forename: Christy G
authors.initials: CG
authors.lastname: Woolcott
authors.forename: Karin R
authors.initials: KR
authors.lastname: Koga
authors.forename: Celia
authors.initials: C
authors.lastname: Byrne
authors.forename: Chisato
authors.initials: C
authors.lastname: Nagata
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
authors.forename: Celine M
authors.initials: CM
authors.lastname: Vachon
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Yaffe
authors.forename: Ian
authors.initials: I
authors.lastname: Pagano
authors.forename: Gertraud
authors.initials: G
authors.lastname: Maskarinec
mesh_terms: D050154:Adiposity; D001741:Black or African American / Q000706:statistics & numerical data; D000368:Aged; D044466:Asian People / Q000706:statistics & numerical data; D015992:Body Mass Index; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000208:ethnology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D016015:Logistic Models; D008327:Mammography; D008875:Middle Aged; D018570:Risk Assessment; D012307:Risk Factors; D044465:White People / Q000706:statistics & numerical data