Effects of parental occupational radiation exposure on offspring: An epidemiological study of cancer incidence trends

Introduction. For many years, the Southern Urals Federal Research and Clinical Center for Medical Biophysics has been analyzing cancer incidence and mortality among Mayak Production Association (Mayak PA) employees and nearby residents. The cohort of Mayak workers’ offspring represents a unique research resource for developing measures to mitigate potential adverse health effects of industrial facilities and improve medical care quality. This is achieved by analyzing the consequences of preconceptional and in utero radiation exposure, with a particular focus on malignancy risk. Previous long-term studies on cancer incidence dynamics among preconceptionally and in utero exposed populations were conducted on smaller sample sizes. Objective. To analyze cancer incidence trends over five-year periods from 1949 to 2020 among the offspring of Mayak PA employees who were exposed to occupational radiation either preconceptionally or during pregnancy. Materials and methods. This retrospective cohort study was based on data from the following sources: Mayak PA Worker Medical and Dosimetry Registry; Ozersk Population Registry (individuals exposed to man-made radiation during childhood due to Mayak PA operations); Ozersk Pediatric Health Registry; Ozersk Cancer Registry; Mayak Worker Dosimetry System — 2013. The analysis included 35 465 individuals, comprising 14 593 offspring of Mayak PA employees who had been exposed to occupational radiation preconceptionally and/or during pregnancy. The control group consisted of 20 872 individuals whose parents had no history of occupational or environmental radiation exposure. In both cohorts, offspring were born between 1949 and 1988 in the closed city of Ozersk, located near the Mayak facility. The follow-up period spanned 72 years. Comparison of incidence rates was performed using the F -test, with statistical significance set at p < 0.05. The average annual percent change (AAPC) in cancer incidence was calculated; trend direction was evaluated by computing a moving average. Results. Among the offspring of exposed fathers, the cancer incidence rate at the end of follow-up was 28.3 cases per 100 000 person-years, with an AAPC in cancer incidence of 19.8%, which exceeds the control group value of 15.0%. Statistically significant differences compared with the control group were identified for male offspring born between 1974 and 1988 during the period from 2001 to 2005 ( F -test = 5.90; p = 0.015). The absolute increase in cancer incidence and the rise in incidence rates among the offspring of exposed fathers are primarily attributed to changes in the age structure of the cohort under study. In the maternal exposure group, the 1949–1953 birth cohort exhibited a significant excess in cancer incidence relative to the control group in 2001–2005 ( F -test = 5.62; p = 0.018). A statistically significant excess was also noted for the 1954–1958 birth cohort during the 1996–2000 follow-up interval ( F -test = 3.98; p = 0.046). Comparison of cancer incidence among the offspring of occupationally exposed fathers versus mothers revealed a significant excess among offspring born between 1964 and 1968 to exposed fathers during the follow-up intervals prior to 1985 ( F -test = 9.26; p = 0.02) and from 1996 to 2000 ( F -test = 5.24; p = 0.022). Periods were identified in 2001–2005 and 2011–2015 during which cancer incidence among female offspring in the maternal exposure group was significantly higher than that in the paternal exposure group ( F -test = 5.96; p = 0.015 and F -test = 5.89; p = 0.015, respectively). Analysis of the moving average revealed a progressive increase in cancer incidence levels among the offspring of exposed parents as the observed cohort aged. Conclusions. The cohorts of offspring from exposed parents are “closed,” which enables a comprehensive epidemiological analysis. Analysis of cancer incidence trends revealed an increase in malignant neoplasms among both the offspring of Mayak PA workers and the control group, a trend most likely attributable to the advancing age of the study cohorts. The statistically significant excess in cancer incidence among the offspring of exposed parents is heterogeneous, which necessitates cautious interpretation. At this stage of the study, these elevated cancer rates cannot be unequivocally linked to radiation exposure, implying the need for further epidemiological monitoring and subsequent calculation of radiation-induced carcinogenic risk estimates.