Multiple Primary Malignant Tumors in Workers Chronically Exposed to Ionizing Radiation

Purpose: To characterize multiple primary malignant tumors (MPMTs) in workers occupationally chronically exposed to ionizing radiation. Material and methods: The study included 22,377 workers employed at reactors, plutonium-production plant and radiochemical plant of the Mayak Production Association (PA) who had been hired in 1948–1982. The study considered cases of MPMTs (verified with the morphological examination) that had been diagnosed in workers before 31 December 2018. The paper describes the structure and provides the comparative characteristics of synchronous and metachronous MPMTs. Results: 320 cases of MPMTs that were verified with the morphological examination were registered in the cohort: 68.4 % in males and 31.6 % in females. 3 and more malignant tumors were registered in 20 % of workers with MPMTs. MPMTs accounted for 10.5 % of total malignant tumors registered in the cohort. Synchronous MPMTs accounted for 22.8 % in males and for 18.8 % in females. 36.6 % of metachronous MPMTs were diagnosed with an interval of more than 10 years. The structure of MPMTs was dominated by tumors of digestive organs, skin, genital organs (both sexes), respiratory organs (for males), and breast (for females). As for a histological type of tumor, adenocarcinomas and basal-cell carcinomas (both sexes), squamous-cell carcinomas (for males), ductal and lobular tumors (for females) were the most frequent. Groups of workers with synchronous and metachronous MPMTs demonstrated some significant differences: synchronous MPMTs were diagnosed in later age than the primary metachronous tumor; the numbers of smokers and heavy alcohol drinkers were bigger in the group of workers with synchronous MPMTs, as well as the smoking index. Neither radiation doses nor the duration of occupational exposure at a date of diagnosis of synchronous MPMTs and a primary metachronous tumor were significantly different. Compared to the entire study cohort, the number of workers occupationally exposed at high doses was bigger in workers with MPMTs (above 1.0 Sv for external gamma-ray exposure, and above 1.0 Gy for internal alpha exposure). Conclusion: MPMTs in workers of the nuclear enterprise were characterized in relation to non-radiation and occupation-related factors. In the future it is planned to assess the impact of the occupational radiation exposure on the risk of MPMTs in workers of the study cohort considering non-radiation factors.