Abstract
BACKGROUND: Thyroid cancer incidence in the United States, particularly in women, has increased dramatically since the 1980s. Although the causes of thyroid cancer in most patients remain largely unknown, evidence suggests the existence of an inherited predisposition to development of differentiated thyroid carcinoma (DTC). Therefore, the authors explored the association between sporadic DTC and family history of cancer. METHODS: In a retrospective hospital-based case-control study of prospectively recruited subjects who completed the study questionnaire upon enrollment, unconditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) as estimates of the DTC risk associated with first-degree family history of cancer. RESULTS: The study included 288 patients with sporadic DTC and 591 cancer-free controls. Family history of thyroid cancer in first-degree relatives was associated with increased DTC risk (adjusted OR, 4.1; 95% CI, 1.7-9.9). All DTC cases in patients with a first-degree family history of thyroid cancer were cases of papillary thyroid carcinoma (PTC) (adjusted OR, 4.6; 95% CI, 1.9-11.1). Notably, the risk of PTC was highest in subjects with a family history of thyroid cancer in siblings (OR, 7.4; 95% CI, 1.8-30.4). In addition, multifocal primary tumor was more common among PTC patients with first-degree family history of thyroid cancer than among PTC patients with no first-degree family history of thyroid cancer (68.8% vs 35.5%, P = .01). CONCLUSIONS: The study suggests that family history of thyroid cancer in first-degree relatives, particularly in siblings, is associated with an increased risk of sporadic PTC.