title: Increasing incidence of pregnancy-associated breast cancer in Sweden.
abstract: OBJECTIVE
  To estimate the incidence of pregnancy-associated breast cancer during different calendar periods and when pregnancy-associated breast cancer was diagnosed in relation to delivery.
  
  
  METHODS
  This was a population-based cohort study using data from Swedish registers between 1963 and 2002, encompassing women aged 15-44 years at the date of breast cancer diagnosis. Outcome measures included incidence of pregnancy-associated breast cancer per 100,000 deliveries, the proportion of pregnancy-associated breast cancer among all breast cancers, and observed-to-expected rates.
  
  
  RESULTS
  Between 1963 and 2002, 1,161 cases of pregnancy-associated breast cancer among a total of 16,620 breast cancers were identified in women aged 15 to 44 years. The incidence of pregnancy-associated breast cancer increased from 16.0 to 37.4 per 100,000 deliveries comparing the first and last calendar periods under study. During pregnancy, the overall incidence was 2.4 per 100,000 deliveries; the incidence during the first and second year after delivery was 10.6 and 15.0 per 100,000 deliveries, respectively. Fewer pregnancy-associated breast cancers than expected were diagnosed during pregnancy and the first 6 months after delivery. Thereafter, there was no difference between observed compared with expected number of breast cancers.
  
  
  CONCLUSIONS
  The incidence of pregnancy-associated breast cancer increased during the study period, partly caused by a trend of postponement of childbearing to an older age. The present findings suggest that breast cancer is underdiagnosed during pregnancy and lactation.
  
  
  METHODS
  III.
authors.affiliation: From the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; the Division of Biostatistics and Epidemiology, UMass Memorial Cancer Center, Worcester, Massachusetts; the Clinical Epidemiology Unit, Department of Medicine, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden; and the Regional Oncologic Center, Uppsala, Sweden.
authors.forename: Therese M-L
authors.initials: TM
authors.lastname: Andersson
authors.forename: Anna L V
authors.initials: ALV
authors.lastname: Johansson
authors.forename: Chung-Cheng
authors.initials: CC
authors.lastname: Hsieh
authors.forename: Sven
authors.initials: S
authors.lastname: Cnattingius
authors.forename: Mats
authors.initials: M
authors.lastname: Lambe
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001943:Breast Neoplasms / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D010298:Parity; D049590:Postpartum Period; D011247:Pregnancy; D011252:Pregnancy Complications, Neoplastic / Q000453:epidemiology*; D012042:Registries; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors; D055815:Young Adult
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