title: Worldwide trends in cervical cancer incidence: impact of screening against changes in disease risk factors.
abstract: BACKGROUND
  Cervical cancer trends in a given country mainly depend on the existence of effective screening programmes and time changes in disease risk factors, notably exposure to human papillomavirus (HPV). Screening primarily influences variations by period of diagnosis, whereas changes in risk factors chiefly manifest themselves as variations in risk across successive birth cohorts of women.
  
  
  METHODS
  We assessed trends in cervical cancer across 38 countries in five continents, age group 30-74 years, using age-standardised incidence rates (ASRs) and age-period-cohort (APC) models. Non-identifiability in APC models was circumvented by making assumptions based on a consistent relationship between age and cervical cancer incidence (i.e. approximately constant rates after age 45 years).
  
  
  RESULTS
  ASRs decreased in several countries, except in most of Eastern European populations, Thailand as well as Uganda, although the direction and magnitude of period and birth cohort effects varied substantially. Strong downward trends in cervical cancer risk by period were found in the highest-income countries, whereas no clear changes by period were found in lower-resourced settings. Successive generations of women born after 1940 or 1950 exhibited either an increase in risk of cervical cancer (in most European countries, Japan, China), no substantial changes (North America and Australia) or a decrease (Ecuador and India).
  
  
  CONCLUSIONS
  In countries where effective screening has been in place for a long time the consequences of underlying increases in cohort-specific risk were largely avoided. In the absence of screening, cohort-led increases or, stable, cervical cancer ASRs were observed. Our study underscores the importance of strengthening screening efforts and augmenting existing cancer control efforts with HPV vaccination, notably in those countries where unfavourable cohort effects are continuing or emerging.
  
  
  BACKGROUND
  Bill and Melinda Gates Foundation (BMGF).
authors.affiliation: International Agency for Research on Cancer, 150 Cours Albert Thomas, 69372 Lyon Cedex 08, France. Electronic address: vaccarellas@iarc.fr.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Vaccarella
authors.forename: Joannie
authors.initials: J
authors.lastname: Lortet-Tieulent
authors.forename: Martyn
authors.initials: M
authors.lastname: Plummer
authors.forename: Silvia
authors.initials: S
authors.lastname: Franceschi
authors.forename: Freddie
authors.initials: F
authors.lastname: Bray
mesh_terms: D000328:Adult; D000368:Aged; D055088:Early Detection of Cancer; D005260:Female; D014943:Global Health; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D012307:Risk Factors; D002583:Uterine Cervical Neoplasms / Q000453:epidemiology*
keywords: Age-period-cohort models; Cervical cancer; Impact of screening; Incidence trends