Non-thyroid cancer incidence in Belarusian residents exposed to Chernobyl fallout in childhood and adolescence: Standardized Incidence Ratio analysis, 1997-2011.

BACKGROUND: While an increased risk of thyroid cancer from post-Chernobyl exposure to Iodine-131 (I-131) in children and adolescents has been well-documented, risks of other cancers or leukemia as a result of residence in radioactively contaminated areas remain uncertain. METHODS: We studied non-thyroid cancer incidence in a cohort of about 12,000 individuals from Belarus exposed under age of 18 years to Chernobyl fallout (median age at the time of Chernobyl accident of 7.9 years). During 15 years of follow-up from1997 through 2011, 54 incident cancers excluding thyroid were identified in the study cohort with 142,968 person-years at risk. We performed Standardized Incidence Ratio (SIR) analysis of all solid cancers excluding thyroid (n=42), of leukemia (n=6) and of lymphoma (n=6). RESULTS: We found no significant increase in the incidence of non-thyroid solid cancer (SIR=0.83, 95% Confidence Interval [CI]: 0.61; 1.11), lymphoma (SIR=0.66, 95% CI: 0.26; 1.33) or leukemia (SIR=1.78, 95% CI: 0.71; 3.61) in the study cohort as compared with the sex-, age- and calendar-time-specific national rates. These findings may in part reflect the relatively young age of study subjects (median attained age of 33.4 years), and long latency for some radiation-related solid cancers. CONCLUSIONS: We found no evidence of statistically significant increases in solid cancer, lymphoma and leukemia incidence 25 years after childhood exposure in the study cohort; however, it is important to continue follow-up non-thyroid cancers in individuals exposed to low-level radiation at radiosensitive ages.

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.