title: Differences in measured mammographic density in the menstrual cycle.
abstract: BACKGROUND
  In premenopausal women, the sensitivity of screening mammography for detecting breast cancer has been reported to be greater in the follicular phase than in the luteal phase of the menstrual cycle, which may be due to differences in mammographic density. To examine this possible effect, we compared mammographic density in premenopausal women who had mammograms at different phases of the menstrual cycle.
  
  
  METHODS
  We recruited premenopausal women ages 40 to 49 years from two mammography units in Toronto, recorded the first day of the last menstrual period (LMP) and measured mammographic density using Cumulus software. We classified the time of the mammography examination as having occurred in one of four intervals, 1 (first week after LMP), 2 (second week after LMP), 3 (third week after LMP) and 4 (>3 weeks after LMP), and compared mammographic density across intervals.
  
  
  RESULTS
  Of the 936 women included in the analysis, 620 were examined by film and 316 by digital mammography. There were small and statistically nonsignificant variations in breast dense, nondense area, and percent density over the menstrual cycle in women examined by film mammography. Marginally significant variation in percent density was observed in the digital subset due to significant differences in the amount of nondense tissue over the menstrual cycle.
  
  
  CONCLUSIONS
  Variations in mammographic density over the menstrual cycle were small and nonsignificant for women examined by either film or digital mammography. Thus, timing of mammography in menstrual cycle is unlikely to have a significant influence in breast cancer detection by screening mammography.
authors: Ontario Cancer Institute/University Health Network, Toronto, Ontario, Canada.
authors: Gayane
authors: G
authors: Hovhannisyan
authors: Lorraine
authors: L
authors: Chow
authors: Alexandra
authors: A
authors: Schlosser
authors: Martin J
authors: MJ
authors: Yaffe
authors: Norman F
authors: NF
authors: Boyd
authors: Lisa J
authors: LJ
authors: Martin
mesh_terms: D000328:Adult; D000367:Age Factors; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000517:prevention & control; D002170:Canada; D005260:Female; D005498:Follicular Phase; D006801:Humans; D008183:Luteal Phase; D008327:Mammography / Q000379:methods*; D008403:Mass Screening; D008597:Menstrual Cycle / Q000502:physiology*; D008875:Middle Aged; D017697:Premenopause; D015203:Reproducibility of Results; D013997:Time Factors