title: Indicators of microbial-rich environments and the development of papillary thyroid cancer in the California Teachers Study.
abstract: BACKGROUND
  Little epidemiologic research has focused on the role of immune function in papillary thyroid cancer risk despite scattered observations suggesting it may be important (e.g., hygiene hypothesis). Here we investigate papillary thyroid cancer risk associated with self-reported living environments across the lifespan reflecting immunologically relevant exposures to microbial-rich environments.
  
  
  METHODS
  Among 61,803 eligible participants in the California Teachers Study cohort, 100 were diagnosed with invasive papillary thyroid cancer between 2005 and 2012. Multivariate Cox proportional hazards regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI).
  
  
  RESULTS
  Living in a rural area during early childhood was associated with significantly reduced risk of developing papillary thyroid cancer as an adult (HR=0.51, 95% CI: 0.28-0.94). Specifically, reduced risks were observed for living within a half mile of hoofed animals (HR=0.47, 95% CI: 0.26-0.84), as was having an indoor dog or cat (HR=0.51, 95% CI: 0.32-0.80). Neither sharing a bedroom or living in a rented home as a child nor attending daycare or kindergarten was associated with reduced risk.
  
  
  CONCLUSIONS
  Early childhood exposures to hoofed animals or indoor furry pets were associated with reduced risk of subsequently developing papillary thyroid cancer.
  
  
  CONCLUSIONS
  Our findings point to immunologically relevant, early-life exposures to microbial-rich environments as potentially important in reducing thyroid cancer risk, consistent with the hygiene hypothesis and suggesting that certain, possibly animal-derived, microbial exposures may be important to immune calibration or priming.
authors.affiliation: Cancer Prevention Institute of California, Fremont, CA, United States; Department of Health Research and Policy and the Stanford Cancer Institute, Stanford University School of Medicine, Palo Alto, CA, United States. Electronic address: tina@cpic.org.
authors.forename: Christina A
authors.initials: CA
authors.lastname: Clarke
authors.affiliation: Cancer Prevention Institute of California, Fremont, CA, United States; Department of Health Research and Policy and the Stanford Cancer Institute, Stanford University School of Medicine, Palo Alto, CA, United States.
authors.forename: Peggy
authors.initials: P
authors.lastname: Reynolds
authors.affiliation: Cancer Prevention Institute of California, Fremont, CA, United States; Department of Health Research and Policy and the Stanford Cancer Institute, Stanford University School of Medicine, Palo Alto, CA, United States.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Oakley-Girvan
authors.affiliation: Department of Preventive Medicine, University of Southern California, Los Angeles, CA, United States.
authors.forename: Eunjung
authors.initials: E
authors.lastname: Lee
authors.affiliation: Division of Cancer Etiology, Department of Population Sciences, City of Hope National Medical Center, Duarte, CA, United States.
authors.forename: Yani
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Cancer Prevention Institute of California, Fremont, CA, United States.
authors.forename: Juan
authors.initials: J
authors.lastname: Yang
authors.affiliation: Cancer Prevention Institute of California, Fremont, CA, United States.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Moy
authors.affiliation: Division of Cancer Etiology, Department of Population Sciences, City of Hope National Medical Center, Duarte, CA, United States.
authors.forename: Leslie
authors.initials: L
authors.lastname: Bernstein
authors.affiliation: Cancer Prevention Institute of California, Fremont, CA, United States.
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Horn-Ross
mesh_terms: D000328:Adult; D000485:Allergens / Q000276:immunology; D000818:Animals; D002140:California / Q000453:epidemiology; D002277:Carcinoma / Q000453:epidemiology*; D002291:Carcinoma, Papillary; D002415:Cats; D002648:Child; D002675:Child, Preschool; D004285:Dogs; D004777:Environment; D005260:Female; D006801:Humans; D061148:Hygiene Hypothesis; D008297:Male; D057805:Pets / Q000276:immunology; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012424:Rural Population; D000077273:Thyroid Cancer, Papillary; D013964:Thyroid Neoplasms / Q000453:epidemiology*
chemical_list: D000485:Allergens
keywords: California; Early-life exposures; Hygiene hypothesis; Microbial exposures; Thyroid cancer