Increase of regional total cancer incidence in north Sweden due to the Chernobyl accident?

Abstract

Study objective: Is there any epidemiologically visible influence on the cancer incidence after the Chernobyl fallout in Sweden? Design: A cohort study was focused on the fallout of caesium-137 in relation to cancer incidence 1988-1996. Setting: In northern Sweden, affected by the Chernobyl accident in 1986, 450 parishes were categorised by caesium-137 deposition: <3 (reference), 3-29, 30-39, 40-59, 60-79, and 80-120 kiloBecquerel/ m2. Participants: All people 0-60 years living in these parishes in 1986 to 1987 were identified and enrolled in a cohort of 1 143 182 persons. In the follow up 22 409 incident cancer cases were retrieved in 1988-1996. A further analysis focused on the secular trend. Main results: Taking age and population density as confounding factors, and lung cancer incidence in 1988-1996 and total cancer incidence in 1986-1987 by municipality as proxy confounders for smoking and time trends, respectively, the adjusted relative risks for the deposition categories were 1.00 (reference <3 kiloBecquerel/m2), 1.05, 1.03, 1.08, 1.10, and 1.21. The excess relative risk was 0.11 per 100 kiloBecquerel/m 2 (95% CI 0.03 to 0.20). Considering the secular trend, directly age standardised cancer incidence rate differences per 100 000 person years between 1988 to 1996 and the reference period 1986-1987, were 30.3 (indicating a time trend in the reference category), 36.8,42.0,45.8,50.1, and 56.4. No clear excess occurred for leukaemia or thyroid cancer. Conclusions: Unless attributable to chance or remaining uncontrolled confounding, a slight exposure related increase in total cancer incidence has occurred in northern Sweden after the Chernobyl accident.