Incidence trend for colorectal cancer in the cohort of workers exposed to ionizing radiation

Abstract

Colorectal cancer is one of the most common malignant neoplasms. Main causes inducing this type of cancer are factors related to the life style and occupational exposures to chemical agents. Some studies demonstrated an association of colorectal cancer incidence and mortality with ionizing radiation. The aim of the present study was to assess the trend in colorectal cancer incidence in a cohort of nuclear workers employed at the Mayak Production Association who had been exposed to ionizing radiation over prolonged periods. The cohort comprised 22,377 workers (25% of females) employed at one of the main plants (reactors, radiochemical and plutonium production plants) of the Mayak Production Association in 1948-1982 who had been externally exposed to gamma rays (cumulative absorbed colon doses were 0–5.85 Gy with the corresponding median dose of 0.16 Gy) and those who had inhaled aerosols containing plutonium particles had been also internally exposed to alpha radiation (cumulative absorbed colon doses were 0–0.18 Gy with the corresponding median dose of 0.0002 Gy). Over the period of 1948–2018, 239 colon cancers and 186 rectum cancers were diagnosed in the study cohort. The incidence of colorectal malignancies among workers of the study cohort was shown to increase with age above 50. Age-standardized incidence rates were higher in males than in females. The time trend analysis of age-standardized rates of colorectal malignancies among workers of the study cohort was performed using a spline regression. The trend of age-standardized rates of colorectal cancer incidence in the Mayak Production Association workers over the analyzed period was nonmonotonic. In general, the average annual percent change of incidence growth for colon cancer was less than 0.1% (for both sexes), while the corresponding estimates for rectum cancer were 1.1% in males and 30.3% in females. To assess the effect of occupational radiation exposure on the incidence of colorectal malignancies, a radiogenic risk analysis that would take into account non-radiation risk factors should be performed.