Increased cancer risk in male hunters compared to the general male population in Northern Sweden after the Chernobyl Nuclear Power Plant accident?

Dose-response analysis of protracted absorbed organ dose and site-specific cancer incidence in Sweden after the Chernobyl nuclear power plant accident

Background

Adult males in Sweden exhibit an increased risk of cancer associated with an increased absorbed dose to the colon from the Chernobyl accident.

Methods

A closed cohort, with information on hunter status, included all individuals living in northern Sweden in 1986. Complete annual information on exposure to 137Cs at the dwelling coordinate was available for a total of 2,104,101 individuals. A nested case-control method with four controls matched for year of cancer diagnosis and year of birth, was used. Individual absorbed organ doses were calculated between 1986 and 2020 including external and internal exposure. Hazard ratios (HR) per mGy with 95% confidence intervals (95% CI) were calculated using conditional logistic regression adjusted for rural/nonrural habitat, education level and pre-Chernobyl cancer incidence 1980 to 1985. A total of 161,325 cancer cases in males and 144,439 in females were included.

Results

The adjusted HR per mGy for all cancer sites combined was 1.027 (95% CI = 1.022, 1.031) in males and 1.011 (95% CI = 1.006, 1.017) in females. In a post hoc analysis accounting for both remaining confounding from hunter lifestyle and the pre-Chernobyl cancer incidence by county, the adjusted HR per mGy for all cancer sites combined was 1.014 (95% CI = 1.009, 1.019) in males and 1.000 (95% CI = 0.994, 1.006) in females. The post hoc analysis suggested an increased risk of cancer in the colon, pancreas, and stomach, respectively, in males, and lymphoma in females.

Conclusions

Increased cancer risk estimates were found for some specific cancer sites but remaining uncontrolled confounding due to hunter lifestyle could not be ruled out.

Cancer incidence in a male adult population in relation to estimated protracted colon dose - A nested case control study in Northern Sweden after the Chernobyl Nuclear Power Plant accident

INTRODUCTION

Uncertainty in the dose-response of low dose radiation raised concern of an increased cancer incidence in Sweden after the Chernobyl Nuclear Power Plant (NPP) accident.

MATERIAL AND METHODS

A closed cohort was created of all males ≥18 years of age living in the Northern Sweden in 1986. In total 826,400 individuals were enrolled including 40,874 hunters. A nested case-control design was used with five controls randomly selected for each cancer case matched on year of diagnosis and year of birth. Individual absorbed colon dose was calculated 1986 to 2015. Allowing for a 5-year latency period Hazard Ratios (HR) per mGy with 95% Confidence Intervals (95% CI) were calculated in a conditional logistic regression adjusted by rural/non-rural living, length of education and pre-Chernobyl cancer incidence 1980 to 1985. A total of 127,109 cancer cases occurred from 1 January 1991 to 31 December 2015. Cancer was classified in: 1) Organ-specific (stomach, colon, liver, lung, prostate, urinary bladder, thyroid and leukaemia), 2) Other and 3) Not previously associated to ionizing radiation.

RESULTS

The average colon dose in cases was 1.77 mGy compared to controls 1.73 mGy. Hunters average colon dose was 2.32 mGy. Organ-specific cancers showed the highest HR per mGy both in the full cohort, adj HR 1.019 (1.014-1.024) and the hunter subcohort, adj HR 1.014 (1.001-1.027) during follow-up 1991 to 2015. Other cancer and Not previously associated with ionizing radiation showed lower HR per mGy. Therefore, the adj HR per mGy for Total cancer, 1.013 (1.009-1.017) was explained by Organ-specific cancer. Increased adj HR per mGy was seen in stomach, colon and prostate cancer, respectively in the full cohort and lung cancer in hunters.

CONCLUSIONS

Some cancer sites previously associated with ionizing radiation showed a positive adjusted HR per mGy both in the full cohort and in the hunter subcohort.