Search

The radiation-related risk of breast cancer among women following the Chornobyl accident remains uncertain. During pregnancy, there is rapid cell proliferation in the breast while radioactive iodine from fallout exposure can concentrate in lactating breast tissues. We conducted a standardized incidence ratio (SIR) analysis of breast cancer in a cohort of 2,631 women who were lactating and/or pregnant at any time during the 2-month period of radioiodine fallout (April 26, 1986–June 30, 1986). There were 37,151 person-years of follow-up, and 26 incident breast cancers were identified through linkage with the National Cancer Registry of Ukraine. Breast cancer rates among pregnant or lactating women were compared to the general population rates, and SIRs were adjusted for oblast, urban/rural, age, and calendar year. The SIR was not significant for women pregnant at the time of the accident (SIR = 0.75; 95% CI 0.44, 1.18) or for women lactating anytime within 2 months of the accident (SIR = 0.96; 95% CI 0.48, 1.68). However, there was a non-significantly elevated risk for women lactating at the time of accident (SIR = 1.30, 95% CI 0.40, 3.01). The increased SIR for breast cancer among lactating women is consistent with the results of a similar study in Belarus and indicates the need to quantify the radiation risk of breast cancer in a larger study of women lactating during the period of fallout exposure. [ABSTRACT FROM AUTHOR]

Background: Pregnancy and lactation may constitute radiation-sensitive reproductive periods due to rapid cell proliferation and concentration of radioiodine in the lactating breast. However, there are limited epidemiological data among women exposed to radiation during these periods.Methods: We examined incidence of breast cancer in a cohort of 3214 women who were pregnant and/or lactating within 2 months (26 April to 30 June 1986) of the Chernobyl accident and residing in contaminated regions of Belarus. There were 33 breast cancers identified through linkage with the Belarusian National Cancer Registry. Breast cancer rates among women who were either pregnant and/or lactating were compared with population rates by calculating standardized incidence ratios (SIR) and 95% confidence intervals (CI) adjusting for attained age, oblast, urban/rural residence and calendar year.Results: Among women who were lactating, we found a greater than 2-fold increased risk of breast cancer compared with the general population, SIR = 2.49 (95% CI: 1.55, 3.75). In contrast, women who were pregnant were not at increased risk (SIR = 0.84 95% CI: 0.46, 1.38). The SIR was highest in women who were exposed at a younger age and at the earliest time period since the accident, though stratified analyses had limited sample sizes.Conclusions: We found a significantly increased risk of breast cancer among women residing in contaminated areas of Belarus who were lactating at the time of the accident and may have had elevated exposure to radioiodine, when compared with the general population. Studies of breast cancer with individual radiation dose estimates among women exposed during lactation are warranted. [ABSTRACT FROM AUTHOR]

Background: While there is a robust literature on environmental exposure to iodine-131 (131I) in childhood and adolescence and the risk of thyroid cancer and benign nodules, little is known about its effects on thyroid volume.Methods: To assess the effect of 131I dose to the thyroid on the volume of the thyroid gland, we examined the data from the baseline screening of the Belarusian-American Cohort Study of residents of Belarus who were exposed to the Chernobyl fallout at ages ≤18 years. Thyroid dose estimates were based on individual thyroid activity measurements made shortly after the accident and dosimetric data from questionnaires obtained 10-15 years later at baseline screening. During baseline screening, thyroid gland volume was assessed from thyroid ultrasound measurements. The association between radiation dose and thyroid volume was modeled using linear regression where radiation dose was expressed with power terms to address non-linearity. The model was adjusted for attained age, sex, and place of residence, and their modifying effects were examined.Results: The analysis was based on 10,703 subjects. We found a statistically significant positive association between radiation dose and thyroid volume (P < 0.001). Heterogeneity of association was observed by attained age (P < 0.001) with statistically significant association remaining only in the subgroup of ≥18 years at screening (P < 0.001). For this group, increase in dose from 0.0005 to 0.15 Gy was associated with a 1.27 ml (95% CI: 0.46, 2.07) increase in thyroid volume. The estimated effect did not change with increasing doses above 0.15 Gy.Conclusions: This is the first study to examine the association between 131I dose to the thyroid gland and thyroid volume in a population of individuals exposed during childhood and systematically screened 10-15 years later. It provides evidence for a moderate statistically significant increase in thyroid volume among those who were ≥ 18 years at screening. Given that this effect was observed at very low doses and was restricted to a narrow dose range, further studies are necessary to better understand the effect. [ABSTRACT FROM AUTHOR]

In April 1986, the Chernobyl nuclear accident resulted in wide-scale contamination of Belarus with significantly elevated levels of radioiodine isotopes, mainly iodine-131 (131I), and long-lived radiocaesium isotopes, mainly caesium-137 (137Cs). Various groups of the population were affected by exposure to ionising radiation, including pregnant women and their foetuses. This paper describes the methods and results related to the establishment of a cohort of 2965 Belarusian people exposed in utero due to Chernobyl fallout. The cohort consists of individuals whose mothers resided in the most radioactively contaminated areas in Belarus at the time of the accident. Prenatal and postnatal doses to the thyroid due to intake of 131I, external irradiation and ingestion of radiocaesium isotopes were estimated for all cohort members. Ongoing research on this unique cohort will provide important information on adverse health effects following prenatal and postnatal exposure to radioiodine and radiocaesium isotopes, for which available epidemiological data are scant. [ABSTRACT FROM AUTHOR]

Several studies reported an increased risk of thyroid cancer in children and adolescents exposed to radioactive iodines, chiefly iodine-131 (131I), after the 1986 Chornobyl (Ukrainian spelling) nuclear power plant accident. The risk of benign thyroid tumors following such radiation exposure is much less well known. We have previously reported a novel finding of significantly increased risk of thyroid follicular adenoma in a screening study of children and adolescents exposed to the Chornobyl fallout in Ukraine. To verify this finding, we analyzed baseline screening data from a cohort of 11,613 individuals aged ≤18 years at the time of the accident in Belarus (mean age at screening = 21 years). All participants had individual 131I doses estimated from thyroid radioactivity measurements and were screened according to a standardized protocol. We found a significant linear dose response for 38 pathologically confirmed follicular adenoma cases. The excess odds ratio per gray of 2.22 (95% confidence interval: 0.41,13.1 ) was similar in males and females but decreased significantly with increasing age at exposure (P< 0.01 ), with the highest radiation risks estimated for those exposed at <2 years of age. Follicular adenoma radiation risks were not significantly modified by most indicators of past and current iodine deficiency. The present study confirms the 131I-associated increases in risk of follicular adenoma in the Ukrainian population and adds new evidence on the risk increasing with decreasing age at exposure. [ABSTRACT FROM AUTHOR]

Background: The excess incidence of thyroid cancer in Ukraine and Belarus observed a few years after the Chernobyl accident is considered to be largely the result of 131I released from the reactor. Although the Belarus thyroid cancer prevalence data has been previously analyzed, no account was taken of dose measurement error. Methods: We examined dose-response patterns in a thyroid screening prevalence cohort of 11,732 persons aged under 18 at the time of the accident, diagnosed during 1996–2004, who had direct thyroid 131I activity measurement, and were resident in the most radio-actively contaminated regions of Belarus. Three methods of dose-error correction (regression calibration, Monte Carlo maximum likelihood, Bayesian Markov Chain Monte Carlo) were applied. Results: There was a statistically significant (p<0.001) increasing dose-response for prevalent thyroid cancer, irrespective of regression-adjustment method used. Without adjustment for dose errors the excess odds ratio was 1.51 Gy− (95% CI 0.53, 3.86), which was reduced by 13% when regression-calibration adjustment was used, 1.31 Gy− (95% CI 0.47, 3.31). A Monte Carlo maximum likelihood method yielded an excess odds ratio of 1.48 Gy− (95% CI 0.53, 3.87), about 2% lower than the unadjusted analysis. The Bayesian method yielded a maximum posterior excess odds ratio of 1.16 Gy− (95% BCI 0.20, 4.32), 23% lower than the unadjusted analysis. There were borderline significant (p = 0.053–0.078) indications of downward curvature in the dose response, depending on the adjustment methods used. There were also borderline significant (p = 0.102) modifying effects of gender on the radiation dose trend, but no significant modifying effects of age at time of accident, or age at screening as modifiers of dose response (p>0.2). Conclusions: In summary, the relatively small contribution of unshared classical dose error in the current study results in comparatively modest effects on the regression parameters. [ABSTRACT FROM AUTHOR]

BACKGROUND Recent studies of children and adolescents who were exposed to radioactive iodine-131 (I-131) after the 1986 Chernobyl nuclear accident in Ukraine exhibited a significant dose-related increase in the risk of thyroid cancer, but the association of radiation doses with tumor histologic and morphologic features is not clear. METHODS A cohort of 11,664 individuals in Belarus who were aged ≤18 years at the time of the accident underwent 3 cycles of thyroid screening during 1997 to 2008. I-131 thyroid doses were estimated from individual thyroid activity measurements taken within 2 months after the accident and from dosimetric questionnaire data. Demographic, clinical, and tumor pathologic characteristics of the patients with thyroid cancer were analyzed using 1-way analysis of variance, chi-square tests or Fisher exact tests, and logistic regression. RESULTS In total, 158 thyroid cancers were identified as a result of screening. The majority of patients had T1a and T1b tumors (93.7%), with many positive regional lymph nodes (N1; 60.6%) but few distant metastases (M1; <1%). Higher I-131 doses were associated with higher frequency of solid and diffuse sclerosing variants of thyroid cancer ( P < .01) and histologic features of cancer aggressiveness, such as lymphatic vessel invasion, intrathyroidal infiltration, and multifocality (all P < .03). Latency was not correlated with radiation dose. Fifty-two patients with self-reported thyroid cancers which were diagnosed before 1997 were younger at the time of the accident and had a higher percentage of solid variant cancers compared with patients who had screening-detected thyroid cancers (all P < .0001). CONCLUSIONS I-131 thyroid radiation doses were associated with a significantly greater frequency of solid and diffuse sclerosing variants of thyroid cancer and various features of tumor aggressiveness. Cancer 2015;121:457-466. © 2014 American Cancer Society. [ABSTRACT FROM AUTHOR]