Are dietary reports in a case-control study on thyroid cancer biased by risk perception of Chernobyl fallout?

Role of DNA Repair Variants and Diagnostic Radiology Exams in Differentiated Thyroid Cancer Risk: A Pooled Analysis of Two Case-Control Studies

BACKGROUND

Given the increased use and diversity of diagnostic procedures, it is important to understand genetic susceptibility to radiation-induced thyroid cancer.

METHODS

On the basis of self-declared diagnostic radiology examination records in addition to existing literature, we estimated the radiation dose delivered to the thyroid gland from diagnostic procedures during childhood and adulthood in two case-control studies conducted in France. A total of 1,071 differentiated thyroid cancer (DTC) cases and 1,188 controls from the combined studies were genotyped using a custom-made Illumina OncoArray DNA chip. We focused our analysis on variants in genes involved in DNA damage response and repair pathways, representing a total of 5,817 SNPs in 571 genes. We estimated the OR per milli-Gray (OR/mGy) of the radiation dose delivered to the thyroid gland using conditional logistic regression. We then used an unconditional logistic regression model to assess the association between DNA repair gene variants and DTC risk. We performed a meta-analysis of the two studies.

RESULTS

The OR/mGy was 1.02 (95% confidence interval, 1.00-1.03). We found significant associations between DTC and rs7164173 in CHD2 (P = 5.79 × 10-5), rs6067822 in NFATc2 (P = 9.26 × 10-5), rs1059394 and rs699517 both in ENOSF1/THYS, rs12702628 in RPA3, and an interaction between rs7068306 in MGMT and thyroid radiation doses (P = 3.40 × 10-4).

CONCLUSIONS

Our results suggest a role for variants in CDH2, NFATc2, ENOSF1/THYS, RPA3, and MGMT in DTC risk.

IMPACT

CDH2, NFATc2, ENOSF1/THYS, and RPA3 have not previously been shown to be associated with DTC risk.

Dietary habits during the 2 months following the Chernobyl accident and differentiated thyroid cancer risk in a population-based case-control study

BACKGROUND

The Chernobyl nuclear power plant accident occurred in Ukraine on April 26th 1986. In France, the radioactive fallout and thyroid radiation doses were much lower than in highly contaminated areas. However, a number of risk projections have suggested that a small excess in differentiated thyroid cancer (DTC) might occur in eastern France due to this low-level fallout. In order to investigate this potential impact, a case-control study on DTC risk factors was started in 2005, focusing on cases who were less than 15 years old at the time of the Chernobyl accident. Here, we aim to evaluate the relationship between some specific reports of potentially contaminated food between April and June 1986 - in particular fresh dairy products and leafy vegetables - and DTC risk.

METHODS

After excluding subjects who were not born before the Chernobyl accident, the study included 747 cases of DTC matched with 815 controls. Odds ratios were calculated using conditional logistic regression models and were reported for all participants, for women only, for papillary cancer only, and excluding microcarcinomas.

RESULTS

The DTC risk was slightly higher for participants who had consumed locally produced leafy vegetables. However, this association was not stronger in the more contaminated areas than in the others. Conversely, the reported consumption of fresh dairy products was not statistically associated with DTC risk.

CONCLUSION

Because the increase in DTC risk associated with a higher consumption of locally produced vegetables was not more important in the most contaminated areas, our study lacked power to provide evidence for a strong association between consumption of potentially contaminated food and DTC risk.