title: Greatly increased occurrence of breast cancers in areas of mammographically dense tissue.
abstract: BACKGROUND
  Mammographic density is a strong, independent risk factor for breast cancer. A critical unanswered question is whether cancers tend to arise in mammographically dense tissue (i.e. are densities directly related to risk or are they simply a marker of risk). This question cannot be addressed by studying invasive tumors because they manifest as densities and cannot be confidently differentiated from the densities representing fibrous and glandular tissue. We addressed this question by studying ductal carcinoma in situ (DCIS), as revealed by microcalcifications.
  
  
  METHODS
  We studied the cranio-caudal and the mediolateral-oblique mammograms of 28 breasts with a solitary DCIS lesion. Two experienced radiologists independently judged whether the DCIS occurred in a mammographically dense area, and determined the density of different areas of the mammograms.
  
  
  RESULTS
  It was not possible to determine whether the DCIS was or was not in a dense area for six of the tumors. Of the remaining 22 lesions, 21 occurred in dense tissue (test for difference from expected taken as the percentage of density of the 'mammographic quadrant' containing DCIS; P < 0.0001). A preponderance of DCIS (17 out of 28) occurred in the mammographic quadrant with the highest percentage density.
  
  
  CONCLUSIONS
  DCIS occurs overwhelmingly in the mammographically dense areas of the breast, and pre-DCIS mammograms showed that this relationship was not brought about by the presence of the DCIS. This strongly suggests that some aspect of stromal tissue comprising the mammographically dense tissue directly influences the carcinogenic process in the local breast glandular tissue.
authors.affiliation: Department of Preventive Medicine, Keck School of Medicine, University of Southern California/Norris Comprehensive Cancer Center, Los Angeles, California, USA. gursin@usc.edu
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
authors.forename: Linda
authors.initials: L
authors.lastname: Hovanessian-Larsen
authors.forename: Yuri R
authors.initials: YR
authors.lastname: Parisky
authors.forename: Malcolm C
authors.initials: MC
authors.lastname: Pike
authors.forename: Anna H
authors.initials: AH
authors.lastname: Wu
mesh_terms: D001940:Breast / Q000473:pathology*; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D002278:Carcinoma in Situ / Q000000981:diagnostic imaging / Q000453:epidemiology*; D044584:Carcinoma, Ductal / Q000000981:diagnostic imaging / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008327:Mammography; D012189:Retrospective Studies