title: Higher incidence of premenopausal breast cancer in less developed countries; myth or truth?
abstract: BACKGROUND
  Fundamental etiologic differences have been suggested to cause earlier onset of breast cancer in less developed countries (LDCs) than in more developed countries (MDCs). We explored this hypothesis using world-wide breast cancer incidence data.
  
  
  METHODS
  We compared international age-standardized incidence rates (ASR) of pre- (<50 years) and postmenopausal (≥50 years) breast cancers as well as temporal trends in ASRs of pre-and postmenopausal breast cancer among selected countries during 1975-2008. We used joinpoint log-linear regression analysis to estimate annual percent changes (APC) for premenopausal and postmenopausal breast cancer in the northern Europe and in Black and White women population in the US.
  
  
  RESULTS
  Premenopausal breast cancers comprised a substantially higher proportion of all incident breast cancers in LDCs (average 47.3%) compared to MDCs (average 18.5%). However, the ASR of premenopausal breast cancer was consistently higher in MDCs (29.4/100,000) than LDCs (12.8/100,000). The ASR of postmenopausal cancer was about five-fold higher in the MDCs (307.6/100,000) than the LDCs (65.4/100,000). The APC of breast cancer in Denmark was substantially higher in postmenopausal (1.33%) than premenopausal cancer (0.98%). Higher incidence of breast cancer among the white than black women in the US was pertained only to the postmenopausal cancer.
  
  
  CONCLUSIONS
  The substantial and consistent lower age-specific incidence of breast cancer in LDCs than in MDCs contradicts the theory of earlier onset. Demographic differences with fewer old women in LDCs and lower prevalence of risk factors of postmenopausal cancer are the most likely explanation to the lower mean age at diagnosis in these countries.
authors.forename: Reza
authors.initials: R
authors.lastname: Ghiasvand
authors.forename: Hans-Olov
authors.initials: HO
authors.lastname: Adami
authors.forename: Iraj
authors.initials: I
authors.lastname: Harirchi
authors.forename: Rahim
authors.initials: R
authors.lastname: Akrami
authors.affiliation: Cancer Research Center, Cancer Institute of Iran, Tehran University of Medical Sciences, Tehran, Iran. kzendeh@tums.ac.ir.
authors.forename: Kazem
authors.initials: K
authors.lastname: Zendehdel
mesh_terms: D000328:Adult; D001741:Black or African American; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D001208:Asia / Q000453:epidemiology; D044466:Asian People; D001943:Breast Neoplasms / Q000175:diagnosis / Q000453:epidemiology* / Q000208:ethnology; D003906:Developing Countries; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D016014:Linear Models; D008875:Middle Aged; D017697:Premenopause / Q000208:ethnology; D012307:Risk Factors; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D044465:White People; D055815:Young Adult