Radiogenic risk of colorectal cancer in the Southern Urals Population Exposed to Radiation Cohort

Abstract

Colorectal cancer (colon, rectum, rectosigmoid and anus) is one of the most frequently registered cancer sites. Apart from main risk factors for the development of cancer of this localization (dietary disorders, obesity, alcohol and tobacco use, contact with certain chemicals), a number of authors have noted in their studies the effect of ionizing radiation. The objective of this study was to directly assess the excess relative risk of colorectal cancer in the population exposed to long-term chronic radiation mainly in the range of low-dose and low  dose  rates.  These  people  are  included  in  the  Southern  Urals  Population  Exposed  to  Radiation  Cohort. Materials and methods: the analytical cohort included 47,282 people, the follow-up period was 63 years (from 1956 to 2018), and the number of person years at risk was 1,292,930. The incidence catchment area includes five Chelyabinsk Oblast raions, the cities of Chelyabinsk and Ozersk. For the period from 1956 to 2018, 462 cases of colon cancer were registered in the follow-up territory. The colon dose was used as a reference dose. The mean absorbed dose was 69 mGy, the maximum dose – 1,824 mGy. The analysis was performed using Epicure statistical package programs by Poisson regression method with a simple parametric model of excess relative risk. Significance of the results was assessed by the maximum likelihood method with 95% probability. Results: In SUPER members, baseline colorectal cancer incidence rates were found to be dependent on such factors as sex (p<0.001), ethnicity (p=0.001), attained age (p<0.001), education (p<0.001), year of birth of cohort members (p<0.001), presence of cancer in first degree relatives (p=0.03). The risk analysis did not reveal statistically significant dose dependence of the excess relative risk of malignant neoplasms of the whole large intestine, as well as no significant dependence of the excess risk of malignant neoplasms of the colon and rectum. The influence of modifying factors on the magnitude of radiogenic risk was evaluated. Assessment of the excess relative risk of colorectal cancer in this cohort is carried out for the first time.