title: Insulin-like growth factor I in pregnancy and maternal risk of breast cancer.
abstract: BACKGROUND
  The role of insulin-like growth factor (IGF)-I in breast cancer remains controversial, despite numerous reports on the association of the hormone with breast cancer or high-risk mammographic densities. We hypothesized that exposure to elevated IGF-I during early pregnancy, a period characterized by intense cell proliferation in the breasts and in the presence of high concentrations of sex steroids, will be associated with increased maternal risk to develop a breast malignancy.
  
  
  METHODS
  The Northern Sweden Maternity Cohort is an ongoing prospective study, collecting blood samples from first-trimester-pregnant women since 1975 as part of screening for infectious diseases. A case-control study (212 cases and 369 controls) was nested among Northern Sweden Maternity Cohort members who delivered singleton babies. RIA was used to measure IGF-I and IGF-II levels. Conditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI).
  
  
  RESULTS
  Breast cancer risk increased with increasing IGF-I (top tertile OR, 1.7; 95% CI, 1.1-2.7). The association was stronger among the primiparous (OR, 2.2; 95% CI, 1.1-4.4) than in the nonprimiparous women (OR, 1.4; 95% CI, 0.7-2.8). Upper-tertile risks seemed to decrease within the <28-, 28 to 33, and >33-year groups of age at sampling, from 2.5 (0.9-7.6) to 2.1 (0.9-5.0) and 1.2 (0.5-2.5), respectively. There was no association of breast cancer with first-trimester-pregnancy IGF-II.
  
  
  CONCLUSIONS
  The study offers further evidence that IGF-I is important in breast cancer. Our findings suggest that the adverse effect of IGF-I on the breast may be stronger before the remodeling of the gland induced by a first pregnancy.
authors.affiliation: Division of Epidemiology, Department of Obstetrics and Gynecology, New York University School of Medicine, 550 First Avenue, NBV 9E2, New York, NY 10016, USA. lukana01@med.nyu.edu
authors.forename: Annekatrin
authors.initials: A
authors.lastname: Lukanova
authors.forename: Paolo
authors.initials: P
authors.lastname: Toniolo
authors.forename: Anne
authors.initials: A
authors.lastname: Zeleniuch-Jacquotte
authors.forename: Kjell
authors.initials: K
authors.lastname: Grankvist
authors.forename: Marianne
authors.initials: M
authors.lastname: Wulff
authors.forename: Alan A
authors.initials: AA
authors.lastname: Arslan
authors.forename: Yelena
authors.initials: Y
authors.lastname: Afanasyeva
authors.forename: Robert
authors.initials: R
authors.lastname: Johansson
authors.forename: Per
authors.initials: P
authors.lastname: Lenner
authors.forename: Göran
authors.initials: G
authors.lastname: Hallmans
authors.forename: Göran
authors.initials: G
authors.lastname: Wadell
authors.forename: Eva
authors.initials: E
authors.lastname: Lundin
mesh_terms: D000293:Adolescent; D000328:Adult; D001943:Breast Neoplasms / Q000097:blood / Q000453:epidemiology / Q000378:metabolism*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008327:Mammography; D010298:Parity; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood; D011446:Prospective Studies; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology
chemical_list: D007334:Insulin-Like Growth Factor I