Family history of malignant and benign thyroid diseases and risk of thyroid cancer: a population-based case-control study in New Caledonia.

Purpose: Exceptionally high incidence rates of thyroid cancer have been observed in New Caledonia, particularly in Melanesian women, but familial aggregation of thyroid diseases in this population is unknown. We study the association between family history of malignant or benign thyroid diseases and non-medullary thyroid cancer in this country. Methods: We conducted a population-based case-control study including 332 cases with papillary or follicular carcinoma diagnosed in 1993-1999 and 412 controls, matched by sex and 5-year age-group. Results: Thyroid cancer was associated with a history of thyroid cancer in first-degree relatives (odds ratio (OR), 3.2; 95 % CI, 1.6-6.2) and with a family history of multinodular goiter (OR, 3.6; 95 % CI, 1.9-7.0). The ORs did not change by age at diagnosis and with the number of affected relatives. The study provides evidence that the familial component of thyroid cancer is particularly strong in men. Thyroid cancer was not associated with a family history of thyroid diseases in Melanesians from the Loyalty Islands, the area with the highest incidence rates for thyroid cancer, possibly indicating a high frequency of genetic susceptibility variants and lack of genetic variation in this population subgroup. Conclusion: Overall our findings confirm an elevated risk of thyroid cancer in individuals with a family history of malignant or benign thyroid diseases, particularly in Melanesians where familial aggregation of thyroid cancer had never been investigated before. The study of genetic variants in candidate susceptibility genes for thyroid cancer may help clarifying the absence of an association in the subgroup of Melanesians from the Loyalty Islands. [ABSTRACT FROM AUTHOR]