Norwegian case-control study testing the hypothesis that seafood increases the risk of thyroid cancer

Association between seafood intake and the risk of thyroid cancer

Background: Previous observational epidemiological studies such as case-control studies and cohort studies have reported inconsistent results regarding the associations between seafood intake and the risk of thyroid cancer. Materials and methods: We searched PubMed and EMBASE in August 2021 using keywords related to seafood intake and thyroid cancer. A pooled odds ratio (OR) or relative risk (RR) with its 95% confidence interval (CI) was calculated. Results: We included 17 observational studies with 13 case-control studies and 4 cohort studies, which included 4,309 thyroid cancer patients among 599,161 participants. In the random effects model meta-analysis of all 17 studies, we found that there was no significant association between seafood intake (highest vs. lowest intake) and the risk of thyroid cancer (OR or RR, 1.01; 95% CI: 0.86 to 1.19; I2=51.4%). Although the associations were not statistically significant, subgroup meta-analyses by study design showed opposite findings: seafood intake decreased the risk of thyroid cancer in case-control studies (OR or RR, 0.94; 95% CI: 0.74 to 1.19; I2=60.6%; n=13) but increased in cohort studies (OR or RR, 1.14; 95% CI: 0.97 to 1.35; I2=0.0%; n=4). Conclusion: The current meta-analysis of observational epidemiological studies found that that overall, there was no significant association between seafood intake and the risk of thyroid cancer. However, given that cohort studies give us a higher level of evidence than case-control studies, further prospective cohort studies are warranted to confirm the association between them.

Elucidating the link between thyroid cancer and mercury exposure: a review and meta-analysis

Mercury (Hg) is a widely distributed and bioavailable metal of public health concern, with many known human toxicities, but data regarding mercury's influence on thyroid cancer (TC) is scarce. Mercury is known to impact several molecular pathways implicated in carcinogenesis, and its proclivity for bioaccumulation in the thyroid suggests a potential modulatory effect. We conducted a literature/systematic review of studies between 1995-2022 intending to define better and establish relationships between these two entities, congregate the evidence for mercury's potential role in thyroid carcinogenesis, and identify populations of interest for further study. Insufficient evidence precludes definitive conclusions on dietary mercury as a TC risk factor; however, several common mechanisms affected by mercury are crucial for TC development, including biochemical, endocrine, and reactive oxygen species effects. Quantitative analysis revealed associations between TC risk and mercury exposure. In three mercury studies, average urine levels were higher in TC patients, with a mean difference of 1.86 µg/g creatinine (95% CI = 0.32-3.41). In two studies investigating exposure to elevated mercury levels, the exposed group exhibited a higher risk of developing TC, with a relative risk of 1.90 (95% CI = 1.76-2.06). In three thyroid tissue studies, mercury levels (ppm) were higher in TC patients, averaging 0.14 (0.06-0.22) in cancerous cases (N = 178) and 0.08 (0.04-0.11) in normal thyroids (N = 257). Our findings suggest an association between mercury exposure and TC risk, implying a possible predisposing factor. Further research is necessary to reveal the clinical relevance of dietary and environmental mercury exposures in TC pathogenesis.

Understanding cancer etiology: A review of the evidence-based Ayurvedic framework of cancer etiologies

Background of the Study

As many as 10 million people have died from cancer globally in 2020, making it the top cause of mortality in the globe. Cancer develops as a result of the multi-stage process by which normal cells convert into tumor cells, progressing from a precancerous lesion to a malignant tumor. By avoiding risk factors and applying existing evidence-based preventative techniques, 30%-50% of malignancies may be averted. In order to avoid cancer, it is essential to know the specific causes of the disease. Nidanas, or etiologies, are well-described in Ayurvedic science. Here, the causes of cancer have been outlined so that the knowledge may be used effectively to avoid the disease.

Aims

Identification of cancer etiologies that have been described in classics. Evidence-based understanding of these etiologies and to comprehend the significance of etiologies in cancer prevention.

Materials and methods

A thorough evaluation of literature, including ancient Ayurvedic classics, modern medical texts, and articles published in reputable journals, was conducted to meet the study's goals and objectives.

Results

According to Ayurveda, there are three distinct phases of tumorigenesis: chronic inflammation, precancerous development, Granthi (a benign glandular swelli ng), and Arbuda (a precancerous tumor) (definite malignancy). A growing body of evidence suggests that the tumor microenvironment, which is predominantly controlled by inflammatory cells, is an essential player in the neoplastic process.

Conclusion

Although inflammation is coming into the picture just now in the contemporary world, Ayurveda has described this as a leading cause 5000 years back. It is evident that diet and lifestyle play a crucial role in the etiology of Shoth (inflammation).

Effect of Cigarette Smoking on Thyroid Cancer: Meta-Analysis

BACKGROUND

Although smoking is generally carcinogenic, its effect on thyroid cancers is still subject to controversy. The purpose of this study was to summarize the role of smoking in relation to thyroid cancer occurrence.

METHODS

We performed a meta-analysis of 24 eligible studies: 21 case-control studies and three prospective cohort studies. The summary odds ratio (OR) and 95% confidence interval (CI) of all studies were acquired based on random effect model. Further subgroup analyses were conducted according to gender, histological type of thyroid cancer, and smoking status of patients for the case-control studies.

RESULTS

The summary effect size indicated a negative association of smoking for thyroid cancer (OR, 0.798; 95% CI, 0.681 to 0.935). From the subgroup analyses for the case-control studies, reduced risk of thyroid cancer was observed in both men (OR, 0.734; 95% CI, 0.553 to 0.974) and women (OR, 0.792; 95% CI, 0.700 to 0.897). The protective effect of smoking was observed in studies in which thyroid cancer was limited to differentiated thyroid cancers (DTCs) (OR, 0.798; 95% CI, 0.706 to 0.902).

CONCLUSION

Our results suggests that smoking may have a protective effect on thyroid cancer, especially on DTCs. Further studies with larger sample sizes should be conducted in elucidating the dose and time dependent effect of smoking on thyroid cancer with specific focus on the types of thyroid cancers.

Major dietary patterns and differentiated thyroid cancer

BACKGROUND

Differentiated Thyroid Cancer (DTC) is the most common endocrine cancer with an increasing trend worldwide. Dietary pattern as a modifiable factor may be associated with DTC.

OBJECTIVE

The present study aimed to evaluate the association between major dietary patterns and risk of DTC.

METHODS

A case control study was conducted among 309 clinic-based participants in northeast of Iran. Dietary data were then collected by a validated Food Frequency Questionnaire (FFQ). Further, codified data were analyzed by factor analysis and logistic regression analysis to identify the dietary patterns and to examine the association between dietary patterns and DTC, respectively.

RESULTS

According to our results, four major dietary patterns including western dietary pattern, traditional dietary pattern, transitional dietary pattern, and healthy dietary pattern were identified. The western dietary pattern was associated with increased odds of DTC after adjustment for potential confounders (OR = 2.79, 95% CI: 1.01-7.74). However, there was no association between other dietary patterns and DTC after adjustment.

CONCLUSIONS

In conclusion, the findings showed that western dietary pattern might be associated with DTC. Further studies are recommended to provide more conclusive evidences about the association between dietary patterns and DTC.

Plasma ω-3 and ω-6 fatty acids in thyroid diseases

The incidences of nodular goiter (NG), thyroid adenoma (TA), and thyroid cancer (TC) are increasing rapidly; however, the etiologies of these diseases remain unclear. The present study aimed to evaluate the differences in plasma fatty acids among these three thyroid diseases to facilitate etiological research. Four ω-3 and seven ω-6 polyunsaturated fatty acids were measured from 97 TC, 14 TA and 11 NG patient plasma samples with gas chromatography-flame ionization detector. Fatty acids levels were expressed as the percentage of each fatty acid out of the total fatty acids evaluated. The present study identified that the level of 22:6n-3 [median, interquartile range (IQR)] was significantly increased in TA (5.2%, 4.3-6.4%) compared with NG (3.6%, 3.1-4.6%) and TC patients (4.2%, 3.2-4.8%). Though not statistically significant, the levels of 20:5n-3 and 22:5n-3 demonstrated a similar pattern. The level of 22:4n-6 expressed (median, IQR) was significantly increased in NG patients (0.21%, 0.18-0.26%) compared with TA (0.16%, 0.15-0.18%) and TC (0.17%, 0.14-0.22%) patients. Furthermore the fatty acids 18:3n-6, 20:2n-6, 20:3n-6, 20:4:6, and 22:5n-6 demonstrated a similar but statistically insignificant pattern. This suggests that different fatty acids exhibit various etiological roles in NG, TA and TC and warrant further study.

Insights into genetic and epigenetic determinants with impact on vitamin d signaling and cancer association studies: the case of thyroid cancer

Vitamin D is a key regulator of calcium metabolism and has been implicated as a cancer preventive agent. However, clinical studies have revealed conflicting results on its cancer preventive properties, attributed in part to multiple metabolic and regulatory factors susceptible to affect individual responses to exogenous vitamin D. Vitamin D is obtained from dietary sources and sun exposure, which depends on numerous parameters such as skin type, latitude, and lifestyle factors. Focusing on thyroid cancer (TC), we document that genetic and epigenetic determinants can greatly impact individual response to vitamin D and may outweigh the classical clinical correlative studies that focus on sun exposure/dietary intake factors. In particular, genetic determinants innate to host intrinsic metabolic pathways such as highly polymorphic cytochromes P450s responsible for the metabolic activation of vitamin D are expressed in many organs, including the thyroid gland and can impact vitamin D interaction with its nuclear receptor (VDR) in thyroid tissue. Moreover, downstream regulatory pathways in vitamin D signaling as well as VDR are also subject to wide genetic variability among human populations as shown by genome-wide studies. These genetic variations in multiple components of vitamin D pathways are critical determinants for the revaluation of the potential preventive and anticancer properties of vitamin D in TC.

Thyroid cancer risk and smoking status: a meta-analysis

PURPOSE

Previous researchers have reported an inverse association between cigarette smoking and thyroid cancer risk. To summarize the role of smoking in relation to thyroid cancer occurrence, we conducted a meta-analysis.

METHODS

We performed a meta-analysis of 31 eligible studies to summarize the data describing the association between thyroid cancer occurrence and smoking. The case-control studies consisted of 6,260 thyroid cancer cases and 32,935 controls. Cohort studies contained 2,715 thyroid cancer patients that participated from recruitment to follow-up. Q-statistic and I (2) statistic were calculated to examine heterogeneity. Summary relative risks (RRs) and 95 % confidence intervals (95 % CIs) were calculated using a random effects model. Potential sources of heterogeneity were investigated via subgroup and sensitivity analyses, and publication biases were estimated.

RESULTS

Thyroid cancer risk was reduced in persons who had ever-smoked (RR = 0.79; 95 % CI 0.70-0.88) compared with never-smokers. However, strong evidence of heterogeneity was found among the investigated studies; therefore, subgroup analyses were conducted according to study type, smoking status, study location, source of controls, sex, and histological type of thyroid cancer. When the data were stratified by smoking status, an inverse association was observed only among current smokers (RR = 0.74; 95 % CI 0.64-0.86), not former smokers (RR = 1.01; 95 % CI 0.92-1.10). An inverse association was observed only in case-control studies (RR = 0.75; 95 % CI 0.66-0.85).

CONCLUSIONS

This meta-analysis of geographically diverse epidemiological data suggests that smoking, particularly current smoking, may influence susceptibility to thyroid cancer. Further well-designed studies with larger sample sizes should be conducted.

Smoking, alcohol and thyroid cancer occurrence: systematic review and meta-analysis of case-control studies

English language case-control studies reporting on the association of thyroid cancer occurrence with smoking and alcohol drinking are summarized. Two independent researchers performed study selection and data extraction. Random effects model was applied and external adjustment was performed to control for important confounders. Twenty reports published between 1987 and 2007 were included in quantitative synthesis. For smoking, mean association was inverse (odds ratio [OR]: 0.785; 95% CI: 0.701-0.879) remaining after adjustment for alcohol drinking; heterogeneity was moderate. For alcohol drinking, mean association was inverse (OR: 0.795; 95% CI: 0.660-0.958) (remaining after adjustment for smoking, OR: 0.832; 95% CI: 0.688-1.007); heterogeneity was large becoming moderate after adjustment. Data from case-control studies identified showed inverse mean association between thyroid cancer occurrence and ever-smoking or ever-drinking alcohol.

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

OBJECTIVES

The present review summarizes epidemiological evidence on risk factors for thyroid cancer (TC), in particular, nutritional factors.

METHODS

Searches of articles on the issue were conducted using MEDLINE.

RESULTS

Exposure to ionizing radiation, particularly during childhood, is the best-established risk factor for TC. There is also a strong association with history of benign nodules/adenoma or goiter. Iodine deficiency may induce an increasing incidence of benign thyroid conditions, but very high iodine intake also affects thyroid function and, possibly, TC risk. Among dietary factors, fish-the major natural source of iodine in human diet-is not consistently related to TC risk. High intake of cruciferous vegetables shows a weak inverse association with TC. Among other food groups, vegetables other than cruciferous are the only food group showing a favorable effect on TC, with an approximate 20% reduction in risk for subjects with the highest consumption. No effect on TC risk of alcohol, coffee, or other food-groups/nutrients emerged. Height and weight at diagnosis show a moderate positive association with TC risk.

CONCLUSION

At present, the only recognized measures for reducing TC risk is to avoid ionizing radiation and iodine deficiency, particularly in childhood and young women, and to increase vegetable consumption.

Persistent, bioaccumulative and toxic substances in fish: human health considerations

Fish are important dietary items that provide essential nutrients. Fish however, bioaccumulate monomethyl mercury (MMHg) and organo-halogenated pollutants (OHP) that are persistent bioaccumulative and toxic substances (PBTS). Unlike man-made OHP, MMHg is mainly of natural origin but background concentrations of aquatic systems are determined by the environmental Hg-methylating potential. Industrial activities can modulate environmental discharges and fish bioaccumulation of PBTS. Fish and seafood consumption are associated with human body load of PBTS, but farming practices that utilize fishmeal increase the terrestrial food chain resulting in farm-animal accumulation of PBTS. These substances are neurotoxic and endocrine active that can impact humans and wild life, but chemical characteristics of MMHg and OHP modulate interactions with animal tissues. MMHg is protein reactive with a faster metabolism (months) than OHP that are stored and slowly (years) metabolized in fat tissues. Except for brain-Hg, neither Hg nor OHP in tissues are markers of toxic effects; however, deficits in neurobehavioral test-scores of children have been shown in some fish-eating populations. These deficits are transient and within normal range, and are not prodromes of neurological diseases. Although population studies show that consumption of fish at current levels of contamination do not explain neurological disorders, endocrine activity remains controversial. Understanding risk of hazard caused by fish-PBTS consumption requires a wide range of expertise. We discuss chemical, toxic, metabolic, and ecological characteristics associated with PBTS in fish. There are proven health outcome derived from fish consumption, while risk of exposure to avoidable PBTS is a chance that can be minimized by societal actions.

Alcohol drinking, tobacco smoking, and anthropometric characteristics as risk factors for thyroid cancer: a countrywide case-control study in New Caledonia

Exceptionally high incidence rates of thyroid cancer are observed in New Caledonia, particularly in Melanesian women. To investigate further the etiology of thyroid cancer and to clarify the reasons of this elevated incidence, the authors conducted a countrywide population-based case-control study in this multiethnic population. The study included 332 cases with histologically verified papillary or follicular carcinoma (293 women and 39 men) diagnosed in 1993-1999 and 412 population controls (354 women and 58 men) frequency matched by gender and 5-year age group. Thyroid cancer was negatively associated with tobacco smoking and alcohol drinking, but no inverse dose-response relation was observed. Height was positively associated with thyroid cancer, particularly in men. Strong positive associations with weight and body mass index were observed in Melanesian women aged 50 years or more, with an odds ratio of 5.5 (95% confidence interval: 1.5, 20.3) for a body mass index of 35 kg/m2 or greater compared with normal-weight women, and there was a clear dose-response trend. This study clarifies the role of overweight for thyroid cancer in postmenopausal women. Because of the high prevalence of obesity among Melanesian women of New Caledonia, this finding may explain in part the exceptionally elevated incidence of thyroid cancer in this group.

A case-control study in Hiroshima and Nagasaki examining non-radiation risk factors for thyroid cancer

BACKGROUND

Because little is known about the etiology of thyroid cancer in Japan, we conducted a case-control study of thyroid cancer and lifestyle and other risk factors. The present report focuses on medical history, family history, smoking and alcohol drinking, and their interactions with radiation exposure.

METHODS

Thyroid cancer cases reported to the Hiroshima and Nagasaki tumor registries during 1970-1986 were histologically reviewed by pathologists. For each of 362 cases with papillary or follicular adenocarcinoma diagnosed at <75 years of age, one control without cancer matched on city, sex, year of birth, and atomic-bomb radiation exposure was selected from the Life Span Study cohort or the offspring cohort. The cohort subjects were residents of Hiroshima and Nagasaki with or without atomic-bomb radiation exposure. Information on risk factors was obtained through a pre-structured interview carried out in 1986-1988.

RESULTS

Analysis using conditional logistic regression showed history of goiter or thyroid nodule and family history of cancer to be significantly associated with an increased odds ratio for thyroid cancer. Smoking and alcohol drinking were significantly and independently associated with a reduced odds ratio. Interaction between smoking and alcohol drinking was not evident based on either an additive model or a multiplicative model. Radiation exposure did not significantly modify the associations between these factors and thyroid cancer risk.

CONCLUSION

History of goiter/nodule and family history of cancer were risk factors for thyroid cancer. Smoking and alcohol drinking were independently associated with reduced risk. Self-reported retrospective information presents some limitations in interpretation of the data.

Risk factors for thyroid cancer: a prospective cohort study

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 follow-up, 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.

The influence of dietary patterns on the development of thyroid cancer

To elucidate the role of diet in the development of thyroid cancer, we conducted a case-control study of 113 persons with histologically-verified thyroid cancer and 138 controls, matched by age, gender and health unit. Socio-economic data, known risk factors and food consumption of more than 100 items were recorded by interviewer-administered prestructured questionnaire. Factor analysis was used to identify possible dietary patterns and logistic regression analysis was used to explore the effect of food items or dietary patterns on thyroid cancer. After adjustment for age, gender, body mass index (BMI), and total energy intake, significant positive associations were observed for pork consumption, while negative ones were observed for tomatoes, lemons and pasta. Dietary patterns of fruits, raw vegetables and mixed raw vegetables and fruits, led to a reduced risk (corresponding odds ratios (ORs) 0.68, 0.71, 0.73) for all thyroid cancers and similar figures were obtained for papillary thyroid cancers. A dietary pattern of fish and cooked vegetables led to an increased risk (OR 2.79) of follicular cancer.

Epidemiology and primary prevention of thyroid cancer

The purpose of this review is to provide an account of our present knowledge about the epidemiology of nonmedullary thyroid carcinoma, to discuss the effects of environment, lifestyle and radiation on the risk of developing thyroid cancer, and to discuss aspects on primary prevention of the disease. In areas not associated with nuclear fallout, the annual incidence of thyroid cancer ranges between 2.0-3.8 cases per 100,000 in women and 1.2-2.6 per 100,000 in men, women of childbearing age being at highest risk. Low figures are found in some European countries (Denmark, Holland, Slovakia) and high figures are found in Iceland and Hawaii. Differences in iodine intake may be one factor explaining the geographic variation, high iodine intake being associated with a slightly increased risk of developing thyroid cancer. In general, lifestyle factors have only a small effect on the risk of thyroid cancer, a possible protective effect of tobacco smoking has been recently reported. Because of the (small) increase in risk of thyroid cancer associated with iodination programs, these should be supervised, so that the population does not receive excess iodine. The thyroid gland is highly sensitive to radiation-induced oncogenesis. This is verified by numerous reports from survivors after Hiroshima and Nagasaki, the Nevada, Novaja Semlja and Marshal Island atmospheric tests, and the Chernobyl plant accident, as well as by investigations of earlier medical use of radiation for benign diseases in childhood. These reports are summarized in the review. There appears to be a dose-response relation for the risk of developing cancer after exposure to radioactive radioiodine. The thyroid gland of children is especially vulnerable to the carcinogenic action of ionizing radiation. Thus, the incidence of thyroid cancer in children in the Belarus area was less than 1 case per million per year before the Chernobyl accident, increasing to a peak exceeding 100 per million per year in certain areas after the accident. It is a social obligation of scientists to inform the public and politicians of these risks. All nuclear power plants should have a program in operation for stockpiling potassium iodide for distribution within 1-2 days after an accident.

Incidence of thyroid cancer in adults recorded by French cancer registries (1978-1997)

This article analyses time trends and geographical variations of thyroid cancer by histological type. Incidence data were provided by 8 French cancer registries over the period 1978-1997, with 3853 adult cases reported. To assess the effects of age, period, cohort and area on incidence, log-linear Poisson regression models were used. Thyroid cancer increased exponentially from the cohort born in 1925. This increase was essentially due to papillary cancer, which increased by 6.2% per year in men and 8.1% per year in women over the entire period (1978-1997). In women, the recent trends were significantly different between the studied geographical areas. The analysis shows that the increase in thyroid cancer, essentially of the papillary type, is not recent. It may be attributed to a possible screening effect or to an increase in the number of "incidentally" discovered cases linked to the use of modern diagnostic tools.

Benign thyroid disease and dietary factors in thyroid cancer: a case-control study in Kuwait

We conducted a population-based study of 313 case-control pairs in Kuwait to examine the aetiology of thyroid cancer, the second most common neoplasm among women in this and several other countries in the Gulf region. Among the demographic variables, individuals with 12+ years of education had a significantly reduced risk of thyroid cancer (OR=0.6; 95% CI: 0.3-0.9). The average age at diagnosis (+/-s.d.) of thyroid cancer was 34.7+/-11 years in women and 39+/-13.4 years in men. History of thyroid nodule was reported only by cases (n=34; 10.9%; lower 95% CI: 12.0); and goitre by 21 cases and four controls (OR=5.3; 95% CI: 1.8-15.3). There was no significant increase in risk with history of hypothyroidism (OR=1.8) or hyperthyroidism (OR=1.7). For any benign thyroid disease, the OR was 6.4 (95% CI: 3.4-12.0); and the population attributable risk was about 26% (95% CI: 21.1-30.9). Stepwise regression analysis showed that high consumption of processed fish products (OR=2.2; 95% CI: 1.6-3.0) fresh fish (OR=0.5; 95% CI: 0.4-0.7) and chicken (OR=1.7; 95% CI: 1.2-2.3) were independently associated with thyroid cancer with significant dose-response relationships. Among the thyroid cancer patients who reported high consumption of fish products, a large majority also reported high consumption of fresh fish (98%) and shellfish (68%). No clear association emerged with consumption of cruciferous vegetables. These data support the hypothesis that hyperplastic thyroid disease is strongly related to thyroid cancer; and that habitual high consumption of various seafoods may be relevant to the aetiology of thyroid cancer. The association with chicken consumption requires further study.

Association between malignant tumors of the thyroid gland and exposure to environmental protective and risk factors

Risk factors for thyroid carcinomas and adenomas were investigated using a standard questionnaire in a case-control study in Southwestern Germany, a known iodine deficiency area. A clinical registry, set up after the Chernobyl accident at the University hospital Mannheim, served as the basis for 174 incident cases of each diagnostic group. Interview data were compared within and with prevalences from a population-based matched control group of equal size from the entire area. The protective role of coffee drinking and the consumption of cruciferous vegetables, such as broccoli, were confirmed for both genders. A high consumption of tomatoes (> 200/year) was associated with an elevated risk of > 2.5 for malignant tumors but not for benign tumors in both genders. In both genders, both treatment for goiter (hyperthyroidism) and decaffeinated coffee consumption were associated with an increased risk for malignant tumors, but less so for adenomas. In women, early menarche (< 13 years) and stillbirth after first pregnancy, as well as hysterectomy, were substantial risk factors. Occupational variables and radiation, including medical indications and mammography, did not reveal particular risks. We did not address the role of regular iodine substitution, but did analyze the consumption of freshwater fish and seafood. Multivariate analyses of the most prominent risk factors confirmed the persistence of tomato consumption as a risk factor. In view of experimental evidence on the carcinogenicity of organophosphates and the neurotoxicant effect of certain agrochemicals on neuroendocrinologically regulated organs, we postulate that in Germany, importing off-season tomatoes from areas with a known history of possible inexperienced use of agrochemicals may be associated with a promoting effect for malignant neoplasias of the thyroid gland in terms of promoting already existent proliferating tissue growth.

Increased risk of thyroid cancer among Norwegian women married to fishery workers--a retrospective cohort study

The relationship between thyroid cancer in women and the occupation of their spouses was examined in a retrospective cohort study, with special reference to fishery. Of the 2.9 million women registered in the Central Population Registry of Norway on 31 December 1991, 1.2 million women had a spouse registered with an occupation in one or more of the censuses in 1960, 1970 or 1980. The women were assigned to ten broad categories based on the first digit of their husbands five-digit Nordic occupational classification code NYK, and a standardized incidence ratio (SIR) was calculated for each occupational category. The women were further subdivided and analysed in 71 groups defined by the first two digits of the NYK code. Among the women included in the study, a total of 2409 cases of thyroid cancer were reported to the cancer registry of Norway during 1960-92. A significantly elevated risk of thyroid cancer was found only among women whose spouses belonged to the occupational category 'agriculture, forestry or fishery' (n = 208 279), with a SIR of 1.13. In the group associated with 'fishing, whaling and sealing work' (n = 40 839), the risk was further increased (SIR 1.91, CI 1.65-2.21). An increased risk was also detected in the group associated with 'ship officers and pilots work' (n = 29 133) (SIR 1.35, CI 1.07-1.67). When allocating the women to southern and northern cohorts determined by their county of birth, a difference in risk was clearly present in all 10 occupational categories, with figures being 50-60% higher in the north. However, there was practically no difference in incidence between northern and southern cohorts among women associated with fishery work. Thus, the results obtained from this study indicate that being a fisherman's wife is associated with elevated risk of thyroid cancer, and our data support the suggested role of seafood as an aetiological factor.

Second primary neoplasms in thyroid cancer patients

To determine risk patterns for second primary neoplasms after the occurrence of thyroid cancer, we conducted a retrospective cohort study of 3321 thyroid cancer patients who were operated and histologically confirmed at the Noguchi Thyroid Clinic and Hospital Foundation between 1946 and 1985. They were followed from the date of operation through the end of 1990 with an observation period from 45 to 5 years. The average observation period of the patients was 13.4 years and the follow-up rate reached 98%. The standardized mortality ratio (SMR) was computed to assess possible risk increase by cancer site. In this computation, the time period less than 5 years after operation was omitted to reduce the influence of deaths related to the original thyroid cancer. A total of 103 deaths from malignant neoplasms other than thyroid cancer were observed during this time period (SMR = 1.6, 95% confidence interval [CI] = 1.3-2.0). Analyses of site-specific cancer mortality revealed significantly elevated risks for the central nervous system (SMR = 16.1, CI = 5.2-37.6) and respiratory organs (SMR = 2.6, CI = 1.5-4.1). Based on a review of available medical records with histological findings, we concluded that the risk increases for these sites were most likely to be attributable to second primary neoplasms. Whether or not the patients had received radiotherapy was not significantly associated with elevated risk. Further investigations are needed to clarify the risk factors responsible for the above findings.

Thyroid Carcinoma in Japan and the West: Similarities and Differences

Geographic or ethnic differences in the incidence of thyroid carcinoma, as well as in the histologic distribution of thyroid carcinoma between Japan and Western countries, have been described but are still unclear. The recent establishment of histologic criteria for the diagnosis of thyroid carcinoma by the WHO committee has facilitated the comparison of clinicopathological data of patients with thyroid carcinoma all over the world. The aim of the present review article is to clarify the epidemiological and clinicopathological differences of thyroid carcinoma between Japan and Western countries. We found recently no significant differences in the incidence, mortality, and histologic distribution of thyroid carcinoma between Japan and Western countries; this was contrary to our expectation. This is likely attributable to westernization of the Japanese diet, standardized medical levels, and international standardization of histologic criteria of thyroid carcinoma.

Study of distribution and interaction of arsenic and selenium in rat thyroid

Seventy-eight Wistar weanling rats were pretreated with arsenate (100 mg/L As), selenite (1 mg/L Se), and arsenate (100 mg/L As) plus selenite (1 mg/L Se) added to the drinking water. After 4 w, all the animals were sacrificed and serum T3 and T4 were determined by double-antibody radioimmunoassay. Thyroid tissue concentrations of As and Se were determined in female rats by neutron activation analysis, and tissue specimens were examined histopathologically. For both sexes, the measurements indicated that T4/T3 was lowest in the Se group, intermediate in the As group, and highest in the controls. Corrected for the mean value of the controls, mean As concentration of thyroid tissue was of the same magnitude in the group pretreated with As + Se as the sum of the mean As concentration in the groups pretreated with As or Se alone. The outcome was symmetric with regard to the Se concentration: In the As + Se pretreated group, the mean Se concentration was of the same magnitude as the sum of the mean Se concentration in the groups pretreated with As or Se alone. Thus, As and Se tended to accumulate in the thyroid tissue. Postmortem examination showed that the thyroid tissue of rats pretreated with As alone exhibited obvious, toxic changes, whereas only minor or no changes were found in the tissues of the groups pretreated with Se or As + Se, and in the tissues of the controls. Multivariate analyses demonstrated that s-T4 and s-T3 were significantly correlated with sex, that s-T3 was positively correlated (p < or = 0.001) with Se pretreatment, and that the T4/T3 ratio was negatively correlated with both As (p < or = 0.012) and Se pretreatment (p < or = 0.001). The results were discussed in relation to the cancer preventive effect of Se.

Longchain serum fatty acids and risk of thyroid cancer: a population-based case-control study in Norway

Epidemiologic studies have shown an association between seafood consumption and risk of thyroid cancer. Fish meals increase the serum concentrations of the longchain fatty acids, eicosapentaenoic acid (20:5,n-3) (EPA) and docosahexaenoic acid (22:6,n-3) (DHA), for days. The hypothesis that serum concentrations of fatty acids may be associated with thyroid cancer risk therefore was tested in a population-based case-control study with 74 cases and 221 matched controls. Seventy-three cases with sera in the Norwegian serum bank (JANUS) were identified in the Norwegian Cancer Registry and matched with three controls, also in JANUS, on age, gender, place of residence, and time of blood sampling. One [corrected] case was matched with two controls. Serum concentrations of 11 longchain fatty acids were determined blindly by gas chromatography for all subjects. Controls were divided into three groups with increasing serum fatty acid concentrations, and odds ratios between cases and controls were estimated relative to the group with lowest serum level by univariate and multivariate analyses. The main finding was a significant inverse relation between the sum of arachidonic acid (20:4,n-6) (AA) and DHA serum concentrations and thyroid cancer risk. The significance of this association was weakened when the analyses were restricted to the papillary type of thyroid carcinoma. It was of the same order of magnitude whether the period between blood sampling and diagnosis was greater than eight years, or eight or less years. High EPA/AA ratio, indicating consumption of fish fat, was not associated significantly with increased thyroid-cancer risk.(ABSTRACT TRUNCATED AT 250 WORDS)

A case-control study of thyroid cancer in women under age 55 in Shanghai (People's Republic of China)

A population-based interview study of 207 case-control pairs investigated reproductive, dietary, and other factors thought likely to increase thyroid cancer risk among women of reproductive age in Shanghai. Of particular interest were factors that might help explain the striking female over male excess in this age group. Risk was strongly associated with prior goiter or benign nodules (odds ratio [OR] = 7.0, 95 percent confidence interval [CI] = 2.5-27.5) and miscarriage as outcome of first pregnancy (OR = 9.9, CI = 2.0-48.4). Weaker associations were seen for women who were ever-pregnant (OR = 2.1, CI = 1.1-4.2), ever had an induced abortion (OR = 1.6, CI = 0.9-2.9), and ever used oral contraceptives (OR = 1.7, CI = 1.0-3.1). Compared with controls, cases gained significantly more weight from menarche to highest nonpregnant weight (P trend < 0.01). Overall, cases ate more fish and shellfish, but there was no trend with level of consumption. More cases had a parent, sibling, or child with thyroid disease (OR = 5.2, CI = 2.5-12.1). Our findings relating to goiter and benign nodules and various reproductive factors support earlier studies. Consumption of seafood was difficult to evaluate; more detailed dietary data are needed to assess iodine intake.