title: Mammographic density and histopathologic characteristics of screen-detected tumors in the Norwegian Breast Cancer Screening Program.
abstract: BACKGROUND
  High mammographic density might mask breast tumors, resulting in delayed diagnosis or missed cancers.
  
  
  OBJECTIVE
  To investigate the association between mammographic density and histopathologic tumor characteristics (histologic type, size, grade, and lymph node status) among women screened in the Norwegian Breast Cancer Screening Program.
  
  
  METHODS
  Information about 1760 screen-detected ductal carcinoma in situ (DCIS) and 7366 invasive breast cancers diagnosed among women aged 50-69 years, 1996-2010, was analyzed. The screening mammograms were classified subjectively according to the amount of fibroglandular tissue into fatty, medium dense, and dense by breast radiologists. Chi-square test was used to compare the distribution of tumor characteristics by mammographic density. Odds ratio (OR) of tumor characteristics by density was estimated by means of logistic regression, adjusting for screening mode (screen-film and full-field digital mammography), and age.
  
  
  RESULTS
  Mean and median tumor size of invasive breast cancers was 13.8 and 12 mm, respectively, for women with fatty breasts, and 16.2 and 14 mm for those with dense breasts. Lymph node positive tumors were identified among 20.6% of women with fatty breasts compared with 27.2% of those with dense breasts (P < 0.001). The proportion of DCIS was significantly lower for women with fatty (15.8%) compared with dense breasts (22.0%). Women with dense breasts had an increased risk of large (OR, 1.44; 95% CI, 1.18-1.73) and lymph node positive tumors (OR, 1.26; 95% CI, 1.05-1.51) compared with women with fatty and medium dense breasts.
  
  
  CONCLUSIONS
  High mammographic density was positively associated with tumor size and lymph node positive tumors.
authors.affiliation: Cancer Registry of Norway, Oslo, Norway.
authors.forename: Nataliia
authors.initials: N
authors.lastname: Moshina
authors.affiliation: Cancer Registry of Norway, Oslo, Norway ; Institute of Basic Medical Sciences, Medical Faculty, University of Oslo, Oslo, Norway ; Department of Preventive Medicine, University of Southern California, California, USA.
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
authors.affiliation: Department of Radiology, Aalesund Hospital, Helse Møre og Romsdal HF, Aalesund, Norway.
authors.forename: Solveig Roth
authors.initials: SR
authors.lastname: Hoff
authors.affiliation: Centre for Cancer Biomarkers CCBIO, Department of Clinical Medicine, Section for Pathology, University of Bergen, Bergen, Norway ; Department of Pathology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Lars A
authors.initials: LA
authors.lastname: Akslen
authors.affiliation: Cancer Registry of Norway, Oslo, Norway ; Department of Women and Children's Health, Oslo University Hospital, Oslo, Norway.
authors.forename: Marta
authors.initials: M
authors.lastname: Roman
authors.affiliation: Cancer Registry of Norway, Oslo, Norway.
authors.forename: Sofie
authors.initials: S
authors.lastname: Sebuødegård
authors.affiliation: Cancer Registry of Norway, Oslo, Norway ; Oslo and Akershus University College of Applied Sciences, Faculty of Health Science, Oslo, Norway.
authors.forename: Solveig
authors.initials: S
authors.lastname: Hofvind
keywords: Breast cancer screening; mammographic density; tumor characteristics