Purpose and methods: We conducted a population-based case-control study of thyroid cancer. Cases were 292 women, aged 15-54 when diagnosed between the years 1980 and 1983 (145 diagnosed in 1980-81 and 147 diagnosed in 1982-83). Female neighborhood controls (n = 292) were matched to each case on birth-year and race.
Results: Among women < 35 years, thyroid disease in first-degree relatives increased thyroid cancer risk [odds ratio (OR) = 2.0, 95% confidence interval (CI) = 1.1-3.7]. Risk was not associated with fish consumption, although high childhood consumption of shellfish decreased thyroid cancer risk (OR = 0.2, 95% CI = 0.05-0.7 for consumption at least a few times weekly). Among papillary thyroid cancers (82% of cases), frequent adult consumption of saltwater fish decreased risk. Cancer risk was reduced with consumption of certain vegetables, wine, and tea. Other dietary variables, including milk, beer and hard liquor, and coffee were not related to thyroid cancer risk. Among the papillary sample, risk increased with longer use of multivitamins (OR = 2.9, 95% CI = 1.2-7.4 for > 10 years of use). Smoking and body mass were not associated with thyroid cancer risk.
Conclusions: These results suggest a role of family history of thyroid disease and certain dietary variables in the etiology of thyroid cancer in adult females.