Exposure to Ionizing Radiation in Adulthood and Thyroid Cancer Incidence
ABSTRACT Recent reviews of the radiation epidemiology literature have concluded that there is little evidence that exposure to ionizing radiation in adulthood causes thyroid cancer. This paper examines the association between radiation dose and thyroid cancer incidence among Japanese survivors who were adults at the time of the atomic bombings of Hiroshima and Nagasaki.
Analyses were conducted using data on cancer incidence during the period 1958-1998 among 59,687 members of the Life Span Study of atomic bomb survivors who were 20 years or older at time of bombings of Hiroshima and Nagasaki. Poisson regression methods were used to derive estimates of associations between thyroid dose in gray (Gy) and thyroid cancer incidence by sex, age at exposure, and time-since-exposure.
The number of thyroid cancer cases among women (n = 241) was nearly 5-fold the number of cases among men (n = 55). Estimated thyroid dose was positively associated with thyroid cancer incidence among women A-bomb survivors (excess relative rate/Gy = 0.70; 90% confidence interval = 0.20-1.46). In contrast, a negative association was observed between thyroid dose and thyroid cancer among men (excess relative rate/Gy = -0.25; <0 to 90% confidence interval = 0.35). The association among women was positive for all time-since-exposure periods examined but tended to diminish in magnitude with time-since-exposure.
Exposure to ionizing radiation in adulthood was positively associated with thyroid cancer among women A-bomb survivors, although the risk seems to be lower than for those exposed to radiation in childhood.
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ABSTRACT: Background. In the last decades, thyroid cancer incidence has continuously and sharply increased all over the world. This review analyzes the possible reasons of this increase. Summary. Many experts believe that the increased incidence of thyroid cancer is apparent, because of the increased detection of small cancers in the preclinical stage. However, a true increase is also possible, as suggested by the observation that large tumors have also increased and gender differences and birth cohort effects are present. Moreover, thyroid cancer mortality, in spite of earlier diagnosis and better treatment, has not decreased but is rather increasing. Therefore, some environmental carcinogens in the industrialized lifestyle may have specifically affected the thyroid. Among potential carcinogens, the increased exposure to medical radiations is the most likely risk factor. Other factors specific for the thyroid like increased iodine intake and increased prevalence of chronic autoimmune thyroiditis cannot be excluded, while other factors like the increasing prevalence of obesity are not specific for the thyroid. Conclusions. The increased incidence of thyroid cancer is most likely due to a combination of an apparent increase due to more sensitive diagnostic procedures and of a true increase, a possible consequence of increased population exposure to radiation and to other still unrecognized carcinogens.Journal of Cancer Epidemiology 05/2013; 2013:965212. DOI:10.1155/2013/965212
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ABSTRACT: Background stratified Poisson regression is an approach that has been used in the analysis of data derived from a variety of epidemiologically important studies of radiation-exposed populations, including uranium miners, nuclear industry workers, and atomic bomb survivors. We describe a novel approach to fit Poisson regression models that adjust for a set of covariates through background stratification while directly estimating the radiation-disease association of primary interest. The approach makes use of an expression for the Poisson likelihood that treats the coefficients for stratum-specific indicator variables as 'nuisance' variables and avoids the need to explicitly estimate the coefficients for these stratum-specific parameters. Log-linear models, as well as other general relative rate models, are accommodated. This approach is illustrated using data from the Life Span Study of Japanese atomic bomb survivors and data from a study of underground uranium miners. The point estimate and confidence interval obtained from this 'conditional' regression approach are identical to the values obtained using unconditional Poisson regression with model terms for each background stratum. Moreover, it is shown that the proposed approach allows estimation of background stratified Poisson regression models of non-standard form, such as models that parameterize latency effects, as well as regression models in which the number of strata is large, thereby overcoming the limitations of previously available statistical software for fitting background stratified Poisson regression models.Biophysik 12/2011; 51(1):15-22. DOI:10.1007/s00411-011-0394-5 · 1.58 Impact Factor
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ABSTRACT: Both external and internal exposure to ionizing radiation are strong risk factors for the development of thyroid tumors. Until now, the diagnosis of radiation-induced thyroid tumors has been deduced from a network of arguments taken together with the individual history of radiation exposure. Neither the histological features nor the genetic alterations observed in these tumors have been shown to be specific fingerprints of an exposure to radiation. The aim of our work is to define ionizing radiation-related molecular specificities in a series of secondary thyroid tumors developed in the radiation field of patients treated by radiotherapy. To identify molecular markers that could represent a radiation-induction signature, we compared 25K microarray transcriptome profiles of a learning set of 28 thyroid tumors, which comprised 14 follicular thyroid adenomas (FTA) and 14 papillary thyroid carcinomas (PTC), either sporadic or consecutive to external radiotherapy in childhood. We identified a signature composed of 322 genes which discriminates radiation-induced tumors (FTA and PTC) from their sporadic counterparts. The robustness of this signature was further confirmed by blind case-by-case classification of an independent set of 29 tumors (16 FTA and 13 PTC). After the histology code break by the clinicians, 26/29 tumors were well classified regarding tumor etiology, 1 was undetermined, and 2 were misclassified. Our results help shed light on radiation-induced thyroid carcinogenesis, since specific molecular pathways are deregulated in radiation-induced tumors.Endocrine Related Cancer 02/2011; 18(1):193-206. DOI:10.1677/ERC-10-0205 · 4.91 Impact Factor