Risk factors for thyroid cancer: A prospective cohort study

Abstract

Given the higher incidence rate of thyroid cancer among women compared to men and evidence that smoking and alcohol consumption may be inversely related to thyroid cancer risk, we examined thyroid cancer risk in association with menstrual, reproductive and hormonal factors, and cigarette and alcohol consumption, in a prospective cohort study of 89,835 Canadian women aged 40-59 at recruitment who were enrolled in the National Breast Screening Study (NBSS). Linkages to national cancer and mortality databases yielded data on cancer incidence and deaths from all causes, respectively, with follow-up ending between 1998 and 2000. Cox proportional hazards models (using age as the time scale) were used to estimate hazard ratios and 95% confidence intervals for the association between each of the potential risk factors and risk of thyroid cancer overall and by the main histologic subtypes. During a mean of 15.9 years of followup, we observed 169 incident thyroid cancer cases. There was no evidence of altered overall thyroid cancer risk with any of the menstrual, reproductive, or hormonal factors. There was evidence of a decreased risk of papillary thyroid cancer among women with 5 or more live births (vs. nulliparous). Age at which smoking commenced, duration of smoking, number of cigarettes smoked per day, pack-years of smoking and alcohol consumption were not associated with altered thyroid cancer risk. The present study provides little support for associations with hormonal factors, smoking, or alcohol consumption, but there is a need for additional prospective data. ' 2005 Wiley-Liss, Inc.Key words: thyroid neoplasms; prospective cohort; reproductive and hormonal risk factors; smoking history; alcohol consumption Thyroid carcinomas are generally rare, with an annual incidence rate of approximately 5.7 per 100,000 in the United States.1 Other than ionizing radiation, the only definitively established risk factor for this disease, 2 little is known about the etiology of thyroid cancer. However, given that the incidence of thyroid cancer is consistently higher in women than in men 3,4 and the finding that estrogen receptors are present in papillary and follicular thyroid carcinomas (the 2 major histologic subtypes of thyroid cancer), 4 it has been hypothesized that hormonal factors may be involved in the etiology of thyroid cancer. Furthermore, there is experimental evidence that elevated thyroid-stimulating hormone (TSH) levels may play a role in the development of thyroid carcinomas 5-9 and epidemiologic evidence that smoking 10-13 and alcohol consumption 14 may be inversely associated with TSH production, which suggests that they might be inversely associated with thyroid cancer risk.The epidemiologic literature regarding the risk of thyroid cancer in association with menstrual and reproductive factors and use of exogenous hormones is based primarily on the results of casecontrol studies, and findings, with respect to the roles of parity, age at first birth, age at menarche, oral contraceptive use, use of hormone re...

Identifying a risk profile for thyroid cancer

“…Twelve out of 13 case-control studies that examined the association between cigarette smoking and thyroid cancer found the risk of thyroid cancer to be decreased by 40% among smokers (26). Cohort studies, including a prospective Canadian one, were unable to demonstrate any association between smoking history and the risk of thyroid cancer (27). In addition, we were not able to find any correlation between smoking, clinical features, parameters of aggressiveness at diagnosis or during follow-up of 248 patients with thyroid nodules, including 67 benign goiters, 13 follicular adenomas, 136 papillary carcinomas and 32 follicular carcinomas, and 277 controls with similar ethnic backgrounds (28).…”

Smoking and susceptibility to thyroid cancer: an inverse association with CYP1A1 allelic variants

“…Indeed, 12 out of 13 case-control studies that examined the association between cigarette smoking and thyroid cancer found the risk of thyroid cancer to be decreased by 40% among smokers (Mack et al 2003). Cohort studies, including a recent prospective Canadian one, were not able to demonstrate any association between smoking history and the risk of thyroid cancer (Iribarren et al 2001, Navarro Silvera et al 2005.…”

Risk factors for thyroid cancer: an epidemiological review focused on nutritional factors

“…The following search terms were included in the strategy: Thyroid The results from 42 original papers contributed to the present review (in some cases more than one paper was published for each study), including: (1) a comprehensive pooled-analysis of individual data from the 14 case-control studies carried out on TC before 1998 and including over 2,725 TC cases (2,247 women and 478 men) and 4,776 controls (3,699 women and 1,077 men) [11,12]; (2) six case-control studies [13][14][15][16][17][18] and three prospective studies published subsequently [19][20][21]. Finally, 17 papers not selected by the search strategy, mainly discussing biological mechanisms, were included in the present review, as well as results from several reviews, related to TC, from the International Agency for Research on Cancer (IARC) and other institutions [1,4,5,[22][23][24][25][26][27][28][29][30].…”