title: An analysis of mass screening strategies using a mathematical model: comparison of breast cancer screening in Japan and the United States.
abstract: BACKGROUND
  Although the United States Preventive Services Task Force (USPSTF) downgraded their recommendation for breast cancer screening for women aged 40-49 years in 2009, Japanese women in their 40s have been encouraged to attend breast cancer screenings since 2004. The aim of this study is to examine whether these different mass-screening strategies are justifiable by the different situations of these countries and to provide evidence for suitable judgment.
  
  
  METHODS
  Performance of screening strategies (annual/biennial intervals; initiating/terminating ages) was evaluated using a mathematical model based on the natural history of breast cancer and the transition between its stages. Benefits (reduced number of deaths and extended average life expectancy) and harm (false-positives) associated with these strategies were calculated.
  
  
  RESULTS
  Additional average life expectancy by including women in their 40s as participants were 13 days (26%) and 25 days (22%) in Japan and the United States, respectively, under the biennial screening condition; however, the respective increases in numbers of false-positive cases were 65% and 53% in Japan and the United States. Moreover, the number of screenings needed to detect one diagnosis or to avert one death was smaller when participants were limited to women of age 50 or over than when women in their 40s were included. The validity of including women in their 40s in Japan could not be determined without specifying the weight of harms compared to benefits.
  
  
  CONCLUSIONS
  Whether screening of women in their 40s in Japan is justifiable must be carefully determined based the quantitative balance of benefits and harms.
authors.affiliation: Department of Health Informatics, Graduate School of Biomedical and Health Sciences Hiroshima University.
authors.forename: Miwako
authors.initials: M
authors.lastname: Tsunematsu
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kakehashi
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000517:prevention & control*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007564:Japan; D008017:Life Expectancy; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D008962:Models, Theoretical; D018570:Risk Assessment; D014481:United States