Anthropometric factors in differentiated thyroid cancer in French Polynesia: a case–control study

[Epidemiology of thyroid carcinoma over the world]

Thyroid cancer (TC) incidence, in France and over the world, has dramatically increased over the last two decades. The temporal and geographical incidence trends in France and in the world are analysed. The increased incidence of TC is actual, mainly due to an increase of papillary microcarcinomas. The spread of ultrasonographic and cytological procedures, the extensiveness of thyroidectomies lead to diagnostic advance, to a better preoperative selection of patients and to the discovery of occult microcarcinomas. Nevertheless, the impact of the risk factors of thyroid cancer on the increase of incidence is not excluded. These risk factors are analysed, especially environmental chemicals agents that disrupt thyroid function.

Obesity and thyroid cancer risk among U.S. men and women: a pooled analysis of five prospective studies

BACKGROUND

Thyroid cancer incidence has risen dramatically in the United States since the early 1980s. Although the prevalence of obesity has doubled during this time period, the relationship between obesity and thyroid cancer is uncertain.

METHODS

We examined the association between body mass index (BMI) and thyroid cancer risk in a pooled analysis of five prospective U.S. studies, including 413,979 women and 434,953 men. Proportional hazards models with attained age as the time metric were adjusted for education, race, marital status, smoking, alcohol intake, and (where appropriate) cohort and sex.

RESULTS

Over follow-up (mean=10.3 years), 768 women and 388 men were diagnosed with thyroid cancer. The risk of thyroid cancer was greater with increasing BMI [per 5 kg/m2: HR in women, 1.16 (95% CI, 1.08-1.24); HR in men, 1.21 (95% CI, 0.97-1.49)]. There was no significant heterogeneity between studies (both P>0.05). For women and men combined, the HRs for overweight (25.0-29.9 kg/m2) and obesity (≥30 kg/m2) compared with normal-weight (18.5-24.9 kg/m2) were 1.20 (95% CI, 1.04-1.38) and 1.53 (95% CI, 1.31-1.79), respectively. We found no significant effect modification by other factors, and the results did not differ significantly by histologic type. A significant positive association for BMI in young adulthood (ages 18-20) with thyroid cancer risk was also observed [per 5-kg/m2 increase: HR, 1.18 (95% CI, 1.03-1.35)].

CONCLUSION

BMI was positively associated with thyroid cancer risk in both men and women.

IMPACT

Our study provides strong evidence that obesity is an independent risk factor for thyroid cancer.

Pooled analysis of two case-control studies in New Caledonia and French Polynesia of body mass index and differentiated thyroid cancer: the importance of body surface area

BACKGROUND

New Caledonia and French Polynesia have among of the world highest thyroid cancer incidence rates. Studies have demonstrated a relationship between anthropometric parameters and the prevalence of cancer. In this study we evaluated further the relationship between body mass index (BMI) and other anthropometric parameters on the incidence of thyroid cancer in the New Caledonia and French Polynesia populations.

METHODS

We performed a pooled analysis of two case-control studies in New Caledonia and French Polynesia. We included a total of 554 cases (65 men and 489 women) of differentiated thyroid cancers and 776 population control subjects matched on sex, age, and study. Anthropometric factors (height, weight, BMI, body fat percentage [BF%], and body surface area [BSA]), at age 18 and before diagnosis, were analyzed by conditional logistic regression, adjusting for other independent risk factors.

RESULTS

A high proportion of cases (73%) were overweight (25-29.9 kg/m(2)) or obese (≥30 kg/m(2)) before diagnosis of thyroid cancer (against 57% of control subjects). An increased risk of thyroid cancer was observed with greater height, weight, BMI, BF%, and BSA. The association of thyroid cancer risk with height, weight, BMI, and BF% did not remain when adjustment was made for BSA. By comparison, the odds ratios for the highest versus the lowest quartile of BSA at age 18 were 3.97 (95% confidence interval, 2.57-6.15; p < 0.001) for women and 4.06 (95% confidence interval, 1.03-16.06; p = 0.04) for men. The association between thyroid cancer risk and each of anthropometric factors did not depend on tumor size or menopausal status before diagnosis.

CONCLUSION

Among anthropometric factors, BSA plays a dominant role in thyroid cancer risk and explains the apparent role of BMI.

Risk factors of thyroid tumors: role of environmental and occupational exposures to chemical pollutants

BACKGROUND

The rising incidence of thyroid cancer observed during the last few decades in most western countries is explained in large part by increasing numbers of diagnoses due to changes in medical screening practices. However, beside radiation exposure, exposure to environmental chemicals may also play a role in thyroid cancer etiology and in the increased incidence. This paper presents the main chemicals suspected to induce thyroid tumorigenesis, and epidemiological results on the association between chemical exposure and thyroid tumors.

METHODS

We reviewed experimental studies to identify the main chemicals possibly involved in thyroid tumorigenesis. We also reviewed the main epidemiological studies investigating the association between environmental chemical exposure and thyroid neoplasm in humans.

RESULTS

Environmentally abundant chemicals may disrupt thyroid function and/or play a role in tumorigenesis through a variety of mechanisms. Epidemiological results provide insufficient evidence of a causal link between exposure to environmental chemicals and thyroid tumors, but raise the hypothesis of an increased risk of thyroid neoplasm for workers in the leather, wood, and paper industries, and those exposed to certain solvents and pesticides.

CONCLUSION

This paper highlights the need for large epidemiological studies evaluating the exposure to various groups of environmental chemicals and its impact on the thyroid gland.

Thyroid cancer following nuclear tests in French Polynesia

BACKGROUND

Between 1966 and 1974, France conducted 41 atmospheric nuclear tests in Polynesia, but their potential health effects have not previously been investigated.

METHODS

In a case-control study, we compared the radiation exposure of almost all the French Polynesians diagnosed with differentiated thyroid carcinoma between 1981 and 2003 (n=229) to the exposure of 373 French Polynesian control individuals without cancer from the general population. Radiation exposures were estimated using measurements after the nuclear tests, age at time of each test, residential and dietary information.

RESULTS

The average thyroid dose before 15 years of age was about 1.8 mGy, and 5% of the cases and 3% of the controls received a dose above 10 mGy. Despite this low level of dose, and after adjusting for ethnic group, level of education, body surface area, family history of thyroid cancer and number of pregnancies for women, we observed an increasing risk (P=0.04) of thyroid cancer with increasing thyroid dose received before age of 15 years, which remained after excluding non-aggressive differentiated thyroid micro-carcinomas. This increase of risk per unit of thyroid radiation dose was higher (P=0.03) in women who later experienced four or more pregnancies than among other women.

CONCLUSION

The risk estimate is low, but is based on limited exposure data. The release of information on exposure, currently classified, would greatly improve the reliability of the risk estimation.

The relationship between body mass index and thyroid cancer pathology features and outcomes: a clinicopathological cohort study

BACKGROUND

Obesity has been implicated as a predisposing and disease-modifying factor in cancer. Epidemiological studies suggest that obesity is associated with an increased risk of thyroid cancer; however, the relationships between obesity and thyroid cancer stage or behavior are uncertain. We hypothesized that a higher body mass index (BMI) would be associated with aggressive thyroid cancer features and a higher incidence of persistent/recurrent disease.

METHODS

Two hundred fifty-nine consecutive patients with thyroid cancer were enrolled in this retrospective cohort study. Histopathological tumor features, stage at diagnosis, and disease status during and at the end of the study were determined based on chart review. BMI was calculated at the first clinical visit to our institution. The relationships between BMI and these parameters were assessed.

RESULTS

Mean follow-up time for the group was 6.2 yr (0.11-46 yr). No positive associations were identified between BMI and T, N, or M stage at diagnosis, vascular invasion, or recurrent or persistent disease on univariate or multivariate analyses. The absence of an association was also demonstrated on analysis by BMI quartiles. An unexpected inverse association was identified between BMI and nodal metastasis and tumor invasion on both univariate and multivariate analyses, suggesting that obesity may be associated with less aggressive tumor features, a finding that requires confirmatory studies.

CONCLUSION

Although obesity has been associated with increased thyroid cancer incidence, a higher BMI was found not to be associated with more aggressive tumor features or a greater likelihood of recurrence or persistence over the analyzed time period.

Risk of differentiated thyroid cancer in relation to adult weight, height and body shape over life: the French E3N cohort

The increasing incidence rate of thyroid cancer warrants investigation of potentially modifiable factors, especially overweightness. Few prospective studies have investigated anthropometry from childhood to adulthood in relation to thyroid cancer. We analyzed data from 91,909 women of the E3N study, a cohort of French women insured by a national health scheme mostly covering teachers with the age of 40-65 years at inclusion in 1990. Risk estimates of first primary differentiated thyroid cancer (n = 317) were computed using Cox proportional hazards models. There was a significant dose-effect relationship between thyroid cancer risk and weight or body mass index (BMI) but not height. Compared with women whose BMI was 18.5-22 kg/m(2), women with BMI 22-25 and those with BMI over 30 had a 39% [95% confidence interval (CI) 7-81] and 76% (12-176) higher risk of thyroid cancer, respectively, with a 21% (5-39) increased risk per 5 kg/m(2) increase in BMI. A large body shape from age 35-40 was significantly associated with an increased risk of differentiated thyroid cancer when compared with a lean one, while earlier body shapes were not. The highest risk was observed in women whose body shape increased from lean to large between menarche and adulthood, with a HR of 2.17 (95% CI 1.04-4.53) when compared with women who were lean at both periods. Our study adds to the existing evidence in relation to excess weight to the risk of thyroid cancer, particularly in women whose body shape increased from menarche to adult age.

Family history of thyroid cancer and the risk of differentiated thyroid cancer in French polynesia

BACKGROUND

Differentiated thyroid carcinoma is considered to be the nonhereditary cancer for which familial inheritance is the highest. To date, no familial aggregation analysis of this cancer has been performed in Maohi populations, which exhibit a very high incidence rate. Therefore, we evaluate the risk of differentiated thyroid cancer associated with a family history of thyroid cancer in natives of French Polynesia.

METHODS

We investigated thyroid cancer incidence in the first-degree relatives of 225 cases of differentiated thyroid carcinomas diagnosed between 1979 and 2004 in patients born in French Polynesia, and 368 randomly selected population controls matched for sex and age, born and residing in French Polynesia. All but five thyroid cancers declared among relatives were validated.

RESULTS

Twenty-four cases declared a family history of thyroid cancer, when compared with 11 controls. Individuals with an affected first-degree relative had a 4.5-fold (95% confidence interval [CI], 1.9-10.6) increased risk of differentiated thyroid cancer. This odds ratio (OR) was not significantly higher when a male first-degree relative was affected (OR, 10.0; 95% CI, 1.3-74.8) compared with a female (OR, 4.0; 95% CI, 1.5-10.3) and was not different for patients who had a nonaggressive thyroid microcarcinoma (OR, 3.5; 95% CI, 0.6-16.4) than those who had a larger cancer (OR, 6.0; 95% CI, 1.8-20.5). This OR was borderline significantly (p, 0.07) higher in Maohis (OR, 11.0; 95% CI, 2.4-48.8) than in individuals of mixed origin (OR, 2.1; 95% CI, 0.8-5.9).

CONCLUSION

Our study shows that the familial inheritance of differentiated thyroid cancer is particularly high in Maohi populations.

[Time trends in the geographic variation of thyroid cancer incidence by tumor size from 1983 to 2000 in France]

BACKGROUND

The aim of this investigation was to study geographic time trends of thyroid cancer incidence according to tumor size in France, 1983 to 2000.

METHODS

Incidence data were provided from six French registries over the period 1983-2000 covering seven administrative districts. Five tumor size groups were distinguished: < 10mm, 10-20mm, 20-40mm, > 40mm and unknown size. Papillary cancers diagnosed in women were analyzed according to tumor size in each geographic area. World age standardized rates were calculated and annual percent change rates were estimated for each tumor size group in each geographic area. Loglinear Poisson regression models were used to study geographic discrepancies in time trends incidences.

RESULTS

The six French registries included 2222 papillary thyroid cancers in women between 1983 et 2000. Thyroid cancer incidence was increasing in the six geographic areas. Geographical variations in time trends incidence between registries reflected geographical variations in time trends incidence of small sized tumors (less than 10mm).

CONCLUSION

Wide geographic variations in thyroid cancer incidence were noticed for small size tumors, which may be correlated with geographic variations in medical practices.

Nonradiation risk factors for thyroid cancer in the US Radiologic Technologists Study

The incidence of thyroid cancer has been rapidly increasing in the United States, but few risk factors have been established. The authors prospectively examined the associations of self-reported medical history, anthropometric factors, and behavioral factors with thyroid cancer risk among 90,713 US radiologic technologists (69,506 women and 21,207 men) followed from 1983 through 2006. Incident thyroid cancers in 242 women and 40 men were reported. Elevated risks were observed for women with benign thyroid conditions (hazard ratio (HR) = 2.35, 95% confidence interval (CI): 1.73, 3.20), benign breast disease (HR = 1.56, 95% CI: 1.08, 2.26), asthma (HR = 1.68, 95% CI: 1.00, 2.83), and body mass index > or =35.0 versus 18.5-24.9 kg/m(2) (HR = 1.74, 95% CI: 1.03, 2.94; P-trend = 0.04). Current smoking was inversely associated with thyroid cancer risk (HR = 0.54). No clear associations emerged for reproductive factors, other medical conditions, alcohol intake, or physical activity. Despite few thyroid cancers in men, men with benign thyroid conditions had a significantly increased risk of thyroid cancer (HR = 4.65, 95% CI: 1.62, 13.34), and results for other risk factors were similar to those for women. Consistent with prior studies, obesity and benign thyroid conditions increased and current smoking decreased the risk of thyroid cancer. The novel findings for benign breast disease and asthma warrant further investigation.

Clinicopathologic significance of leptin and leptin receptor expressions in papillary thyroid carcinoma

BACKGROUND

Epidemiologic studies have shown that obesity is associated with an increased risk of thyroid cancer. Leptin, an adipocyte-derived cytokine, can act as a growth factor on certain normal and transformed cells. Aberrant expression of leptin or leptin receptor has been detected in some types of cancer. The aim of this study is to determine immunohistochemical expression of leptin and leptin receptor in papillary thyroid cancer to investigate the relationship between their expression and clinicopathologic features.

METHODS

The expression of leptin and leptin receptor was assessed in 49 primary neoplasms and 15 lymph node metastases using a semiquantitative immunohistochemical staining method.

RESULTS

Leptin and leptin receptor were expressed in 37% and 51% of papillary thyroid cancer, respectively. They were not expressed in normal follicles. In the primary neoplasms and the metastatic nodes, expression of leptin correlated closely with leptin receptor (P < .001 for the primary neoplasms and P = .017 for nodal metastases). Expression of either protein was associated with greater neoplasm size (leptin expression, 32.0 +/- 10.7 vs 20.5 +/- 8.4 mm; P = .001; leptin receptor expression, 27.9 +/- 11.5 vs 21.4 +/- 9.0 mm; P = .032). Coexpression of leptin and leptin receptor in primary neoplasms had greater incidence of lymph node metastasis (P = .038).

CONCLUSION

Expression of leptin and/or leptin receptor in papillary thyroid cancer is associated with neoplasm aggressiveness, including tumor size and lymph node metastasis.