title: The Role of Oral Contraceptive Pills on Increased Risk of Breast Cancer in Iranian Populations: A Meta-analysis.
abstract: BACKGROUND
  Cancer is one of the main public health issues in the world. Breast cancer is one of the most common types of cancer among women. It is also the second cause of mortality in women. The association between the use of oral contraceptive pills and breast cancer is controversial and a main issue in public health. Some findings have shown that taking these pills does not have a significant effect in increasing the risk of breast cancer, while others have confirmed the carcinogenic effect of these products. These contradictory findings necessitated this meta-analysis, through of all correlated studies in Iran.
  
  
  METHODS
  All published studies were considered from June 2000 until June 2015, using reliable Latin databases like PubMed, Google Scholar, Google search, Scopus, and Science Direct, and Persian database like SID, Irandoc, IranMedex, and Magiran. Finally, 26 papers were selected: 24 studies were case control while two were population based studies. A total of 26 papers with 46,260 participants were assessed since 2001.
  
  
  RESULTS
  Overall estimate of OR for the effect of oral contraceptive pills on breast cancer is 1.521 (CI = 1.25-1.85), which shows that the intervention group had more chance (52%) compared to the control group (P= 0.001). Using these pills increased the risk of breast cancer up to 1.52 times.
  
  
  CONCLUSIONS
  Because of directly increasing levels of estrogen and the role of estrogen in gaining weight indirectly, oral contraceptive pills can stimulate the occurrence of breast cancer. More studies should be conducted for controlling the period of pill use.
authors.affiliation: Lifestyle Modification Research Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran.
authors.forename: Ali
authors.initials: A
authors.lastname: Soroush
authors.affiliation: Cancer Research Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran.
authors.forename: Negin
authors.initials: N
authors.lastname: Farshchian
authors.affiliation: Clinical Research Development Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran.
authors.forename: Saeid
authors.initials: S
authors.lastname: Komasi
authors.affiliation: HSR unit of Treatment Deputy, Kermanshah University of Medical Sciences, Kermanshah, Iran.
authors.forename: Neda
authors.initials: N
authors.lastname: Izadi
authors.affiliation: Cancer Research Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran.
authors.forename: Nasrin
authors.initials: N
authors.lastname: Amirifard
authors.affiliation: Clinical Research Development Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran.
authors.forename: Afshar
authors.initials: A
authors.lastname: Shahmohammadi
keywords: Breast neoplasms; Iran; Meta-analysis; Oral contraceptive