Risks of incidence of breast cancer in a cohort of females occupationally exposed to ionizing radiation

Breast cancer (BrCa) holds the first rank place in morbidity and mortality due to malignant neoplasms among Russian women. BrCa is a multifactorial disease and ionizing radiation is among factors that cause elevated risks of developing BrCa. Our research aim was to assess relative risk (RR) of incidence of BrCa among women who were occupationally exposed to chronic ionizing radiation taking into account radiation and non-radiation factors. RR of incidence of BrCa was analyzed in a cohort of women employed at a nuclear production enterprise, namely Mayak PA, in 1948-1982. 95 % of women started working at the enterprise at their reproductive age. All those women were chronically exposed to ionizing radiation at their workplaces. A mean cumulative breast absorbed dose of external gamma-ray exposure amounted to 0.45 (standard deviation was 0.68) Gy; an average cumulative muscle absorbed dose of internal alpha-particle exposure amounted to 0.003 (0.01) Gy. According to data taken from “Clinic” medical-dosimetric database, 165 BrCa cases were detected in 157 women of the analyzed cohort (8 women had BrCa in both breasts). Our analysis involved calculating RR of incidence of BrCa in relation to known non-radiation and radiation factors. Categorical data analysis was performed without age-related and calendar period-related stratification and with them. RR was analyzed based on Poisson regression with AMFIT module in EPICURE software package. Incidence of BrCa was revealed to be associated with attained age, age of menarche, age of menopause, number of abortions, age of concomitant diseases prior to cancer diagnosis, height, body mass index, age of hiring at the Mayak PA. There was no relationship between BrCa incidence and cumulative doses of occupational chronic external gamma-ray, internal alpha-particle and neutron exposure.