The risk of colorectal cancer incidence in a cohort of individuals occupationally exposed to ionizing radiation

The increased risk of colorectal cancer following ionizing radiation exposure was demonstrated in a number of epidemiological studies. Earlier, no impact of occupational radiation exposure on colorectal cancer incidence or mortality was observed in a cohort of workers of the nuclear industrial facility, Mayak Production Association (PA). Extension of the follow-up of the cohort and improvement of dose estimates for personnel made it possible to update the earlier findings.

The study objective is to assess the risk of colorectal cancer incidence associated with chronic occupational radiation exposure taking into account non-radiation factor effects.
The study cohort included 22,377 workers employed at the reactor, plutonium-producing and radiochemical plants of Mayak PA (hiring period 1948–1982; follow-up period ended on December 31, 2018). Using the Poisson regression (EPICURE software), the relative risks (RRs with 95 % confidence intervals, (95 % CI)) of colorectal cancer incidence were estimated depending on the most significant non-radiation factors (sex, age, smoking, alcohol consumption, excessive body mass and obesity, intestinal polyps, chronic colitis). These values were also calculated for certain ranges of occupational exposure doses relying on data provided by ‘The Mayak Worker Dosimetry System – 2013’. The linear model was used to analyze the dose-response relationship.

In the study cohort, the RR of colorectal cancer incidence was lower in females than in males: 0.72 (95 % CI: 0.55; 0.96) for colon and 0.48 (95 % CI: 0.34; 0.67) for rectum. The increased RR of the rectum cancer incidence was observed for cases with intestinal polyps: 3.42 (95 % CI: 1.68; 6.19). The colon cancer incidence risk increased with increasing age of workers, but other non-radiation factors were not shown to affect the results. This study supported the earlier results: no association was observed between the risk of colorectal cancer incidence and doses of occupational external gamma-ray or internal alpha-particle exposures.