Risk of thyroid cancer among chernobyl liquidators.

After the Chernobyl accident in 1986, the "liquidators" or clean-up workers were among those who received the highest radiation doses to the thyroid from external radiation. Some were also exposed to radioiodines through inhalation or ingestion. A collaborative case-control study nested within cohorts of Belarusian, Russian and Baltic liquidators was conducted to evaluate the radiation-induced risk of thyroid cancer. The study included 107 cases and 423 controls. Individual doses to the thyroid from external radiation and from iodine-131 ((131)I) were estimated for each subject. Most subjects received low doses (median 69 mGy). A statistically significant dose-response relationship was found with total thyroid dose. The Excess Relative Risk (ERR) per 100 mGy was 0.38 [95% confidence interval (CI): 0.10, 1.09]. The risk estimates were similar when doses from (131)I and external radiation were considered separately, although for external radiation the ERR was not statistically significantly elevated. The ERR was similar for micro carcinomas and larger size tumors, and for tumors with and without lymph node involvement. Although recall bias and uncertainties in doses could have affected the magnitude of the risk estimates, the findings of this study contribute to a better characterization the risk of thyroid cancer after radiation exposure in adulthood.

Risk of hematological malignancies among Chernobyl liquidators.

A case-control study of hematological malignancies was conducted among Chernobyl liquidators (accident recovery workers) from Belarus, Russia and Baltic countries to assess the effect of low- to medium-dose protracted radiation exposures on the relative risk of these diseases. The study was nested within cohorts of liquidators who had worked around the Chernobyl plant in 1986-1987. A total of 117 cases [69 leukemia, 34 non-Hodgkin lymphoma (NHL) and 14 other malignancies of lymphoid and hematopoietic tissue] and 481 matched controls were included in the study. Individual dose to the bone marrow and uncertainties were estimated for each subject. The main analyses were restricted to 70 cases (40 leukemia, 20 NHL and 10 other) and their 287 matched controls with reliable information on work in the Chernobyl area. Most subjects received very low doses (median 13 mGy). For all diagnoses combined, a significantly elevated OR was seen at doses of 200 mGy and above. The excess relative risk (ERR) per 100 mGy was 0.60 [90% confidence interval (CI) -0.02, 2.35]. The corresponding estimate for leukemia excluding chronic lymphoid leukemia (CLL) was 0.50 (90% CI -0.38, 5.7). It is slightly higher than but statistically compatible with those estimated from A-bomb survivors and recent low-dose-rate studies. Although sensitivity analyses showed generally similar results, we cannot rule out the possibility that biases and uncertainties could have led to over- or underestimation of the risk in this study.

TP53 codon 72 polymorphism in radiation-associated human papillary thyroid cancer.

The study investigated an association between the germline polymorphism at TP53 codon 72 and the development of papillary thyroid cancer (PTC) following exposure to radiation from the Chernobyl accident. TP53 genotype was examined in 48 pediatric/adolescent (age at diagnosis <18 years) and 68 adult post-Chernobyl patient with PTC, 53 adult patients with sporadic PTC and 313 healthy individuals from Russian-Ukrainian population. In addition, we evaluated loss of heterozygosity for TP53 and the allele expression ratio. The genotype of the patients was correlated with clinicopathological data. Arg TP53 homozygotes were found to be significantly underrepresented among adults with post-Chernobyl PTC, but not in children and adolescents when compared with sporadic PTC cases and the general population. In the tumors, cell transformation did not lead to allelic loss or biased TP53 allele expression in heterozygous individuals. None of TP53 genotypes specifically associated with tumor stage and morphology, however there were particular correlations with lymph node status in certain age groups of radiation-associated cases not seen in sporadic PTCs. The findings suggest TP53 allele combinations other than Arg/Arg may contribute to the risk of development of PTC in individuals exposed to radiation during their late childhood, adolescence or in young adulthood.