Breast cancer trends in two oblasts of Belarus and the Chernobyl accident.

The 1986 Chernobyl accident contaminated 23% of Belarus with radioactive iodine and long half-life radionuclides. Radiation causes breast cancer. Population-based breast cancer incidence data from the Belarus National Cancer Registry were used to study secular trends and urban-rural differences, and determine whether an effect of Chernobyl radiation exposure was discernable. Trends in age-standardized incidences in Gomel and Vitebsk oblasts maximally and minimally exposed to Chernobyl radiation, respectively, were compared for 1978-2003 among all women, and women aged 30-49, separately for urban and rural areas. Incidences were higher and increasing more rapidly in urban than rural areas of both oblasts, annually increasing 0.150 +/- 0.008 vs. 0.098 +/- 0.007 new cases per 10,000 persons, p < 0.00005. Levels were similar in urban Gomel and Vitebsk, and slightly higher in rural Vitebsk than rural Gomel. For ages 30-49 trends in urban and rural Gomel and rural Vitebsk were similar to the all-ages rural trend: common urban/rural Gomel slope 0.098 +/- 0.015, rural Vitebsk slope 0.091 +/- 0.022. In urban Vitebsk, significant but erratic nonlinearity suggested stabilizing incidence since the mid-nineties after a sharp rise. However, recent declines in slopes, greater in Vitebsk, are nonsignificant. Secular breast cancer increases in Gomel have been generally consistent for 26 years. Secular increases in Vitebsk have been similar, but could be slowing. However, these data provide no convincing evidence for Chernobyl-induced breast cancer in Belarus.