Predictors for thyroid carcinoma in Israel: a national cohort of 1,624,310 adolescents followed for up to 40 years.
BACKGROUND
Data on adolescent precursors of thyroid cancer in adulthood are scant.


METHODS
In order to evaluate potential risk factors for thyroid cancer, we linked two national data sources: the military recruitment health examinations and the Israel National Cancer Register. The study population (1,624,310 participants) included 1,145,865 Jewish males aged 16-19 years when examined between 1967 and 2005, and 478,445 Jewish females aged 16-19 years when examined between 1989 and 2005. The cancer follow-up extended up to 2006. Multivariable Cox proportional hazards modeling was used.


RESULTS
During 24,389,502 person years of follow-up, 760 incidence cases of thyroid cancer were identified. The mean age at diagnosis was 25.2±4.2 years for women and 37.2±10.0 years for men. Women had a substantially higher incidence (birth cohort-adjusted hazard ratio (HR)=5.70 [95% CI 4.45-7.31]; p<0.001). Height predicted incidence in both sexes, with birth cohort-adjusted HRs of 1.03 (p<0.001) in males and 1.04 (p<0.001) in females, per 1 cm increment in height. In males, but not in females, there was a graded association between education, as measured by years of schooling, and incidence of thyroid cancer. Body mass index was not associated with incidence. In a multivariable analysis of 617,613 males and 469,185 females examined from 1989 onwards, which included sex, birth year, height, and education, the excess risk in females persisted strongly (HR=5.67 [CI 4.30-7.13]), as did the association with height.


CONCLUSIONS
Female sex, measured height in adolescence, and later birth cohorts were independent predictors of thyroid cancer in young and middle-aged adults in Israel. Further study is needed to unravel the mechanisms whereby height is associated with thyroid cancer.
1 Institute for Endocrinology and Diabetes , National Center for Childhood Diabetes, Schneider Children's Medical Center of Israel, Petach Tikva, Israel .
Alon
A
Farfel
Jeremy D
JD
Kark
Estela
E
Derazne
Dorit
D
Tzur
Micha
M
Barchana
Liora
L
Lazar
Arnon
A
Afek
Ari
A
Shamiss
D000293:Adolescent; D000328:Adult; D001827:Body Height; D015992:Body Mass Index; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007557:Israel / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013964:Thyroid Neoplasms / Q000453:epidemiology / Q000209:etiology*