title: Hormonal factors and the risk of papillary thyroid cancer in the California Teachers Study cohort.
abstract: BACKGROUND
  Despite the increasing incidence of thyroid cancer, there is limited information on its etiology. The strikingly higher rates in young women, compared with men, suggest that sex steroid hormones may be involved in the development of this disease.
  
  
  METHODS
  We investigated the effects of menstrual, reproductive, and other hormonal factors on papillary thyroid cancer risk in the prospective California Teachers Study cohort. Among 117,646 women, 233 were diagnosed with invasive histologically confirmed papillary thyroid cancer after cohort enrollment and before January 1, 2008. Relative risks (RR) and 95% CIs were estimated by using Cox proportional hazards regression models.
  
  
  RESULTS
  Among younger women (age <45 years at baseline; approximately one-third of the cohort), but not older women, later age at menarche (age ≥14 years) was associated with increased risk (RR = 1.88, 95% CI: 1.13-3.13; p(interaction) by age = 0.06). Risk was also increased among young women who had longer (>30 days) adolescent menstrual cycles (RR = 1.78, 95% CI: 1.01-3.14) and whose last pregnancy had ended within five years of cohort enrollment (RR = 2.21, 95% CI: 1.13-4.34). Among older women (age ≥45 years at baseline), ever use of estrogen-only therapy was associated with a statistically nonsignificant increase in risk (RR = 1.69, 95% CI: 0.95-2.98).
  
  
  CONCLUSIONS
  The findings from this prospective analysis suggest that several factors related to delayed pubertal development and the transient effects of pregnancy may be particularly important in influencing risk in young women.
  
  
  CONCLUSIONS
  These results suggest the importance of future research into the role of progesterone and the estrogen-to-progesterone ratio.
authors.affiliation: Cancer Prevention Institute of California, Fremont, CA 94538, USA. pam@cpic.org
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Horn-Ross
authors.forename: Alison J
authors.initials: AJ
authors.lastname: Canchola
authors.forename: Huiyan
authors.initials: H
authors.lastname: Ma
authors.forename: Peggy
authors.initials: P
authors.lastname: Reynolds
authors.forename: Leslie
authors.initials: L
authors.lastname: Bernstein
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002140:California / Q000453:epidemiology; D002291:Carcinoma, Papillary / Q000453:epidemiology* / Q000209:etiology / Q000378:metabolism*; D015331:Cohort Studies; D005260:Female; D012739:Gonadal Steroid Hormones / Q000378:metabolism*; D020249:Hormone Replacement Therapy / Q000706:statistics & numerical data; D006801:Humans; D008572:Menarche; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D018426:SEER Program; D013964:Thyroid Neoplasms / Q000453:epidemiology* / Q000209:etiology / Q000378:metabolism*; D055815:Young Adult
chemical_list: D012739:Gonadal Steroid Hormones