title: Breast cancer incidence after hormonal infertility treatment in Sweden: a cohort study.
abstract: OBJECTIVE
  To assess the impact of infertility treatment with causes of infertility on incidence of breast cancer.
  
  
  METHODS
  Historical prospective cohort study of 1135 women attending major university clinics for treatment of infertility in Sweden, 1961-1976. Women were classified as users of clomiphene citrate or gonadotropins, or a combination of both therapies. Standardized incidence ratios were calculated to estimate relative risk of breast cancer.
  
  
  RESULTS
  We observed 54 cases of breast cancer during 1961-2004, which did not significantly exceed those expected. Users of high-dose clomiphene citrate had an almost 2-fold increased risk (standardized incidence ratio, 1.90; 95% confidence interval, 1.08-3.35). This association was more pronounced among women referred for nonovulatory factors, with 3-fold increased risk (standardized incidence ratio, 3.00; 95% confidence interval, 1.35-6.67).
  
  
  CONCLUSIONS
  No overall increased risk for breast cancer was shown with infertility treatment. Women with nonovulatory causes treated with high-dose clomiphene citrate therapy may have an elevated risk for breast cancer.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden. Chantal.Orgeas@ki.se
authors.forename: Chantal C
authors.initials: CC
authors.lastname: Orgéas
authors.forename: Karin
authors.initials: K
authors.lastname: Sanner
authors.forename: Per
authors.initials: P
authors.lastname: Hall
authors.forename: Peter
authors.initials: P
authors.lastname: Conner
authors.forename: Jan
authors.initials: J
authors.lastname: Holte
authors.forename: Staffan J
authors.initials: SJ
authors.lastname: Nilsson
authors.forename: Karin
authors.initials: K
authors.lastname: Sundfeldt
authors.forename: Ingemar
authors.initials: I
authors.lastname: Persson
authors.forename: Kee Seng
authors.initials: KS
authors.lastname: Chia
authors.forename: Sara
authors.initials: S
authors.lastname: Wedren
authors.forename: Paul W
authors.initials: PW
authors.lastname: Dickman
authors.forename: Kamila
authors.initials: K
authors.lastname: Czene
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000139:chemically induced* / Q000453:epidemiology; D006063:Chorionic Gonadotropin / Q000009:adverse effects* / Q000627:therapeutic use; D002996:Clomiphene / Q000009:adverse effects* / Q000627:therapeutic use; D015331:Cohort Studies; D005260:Female; D005300:Fertility Agents, Female / Q000009:adverse effects* / Q000627:therapeutic use; D006801:Humans; D015994:Incidence; D007247:Infertility, Female / Q000188:drug therapy*; D011446:Prospective Studies; D013548:Sweden / Q000453:epidemiology
chemical_list: D006063:Chorionic Gonadotropin; D005300:Fertility Agents, Female; D002996:Clomiphene