Arsenic trioxide is effective in treating promyelocytic leukemia, and laboratory studies demonstrate that arsenic trioxide causes apoptosis of human breast cancer cells . Region II in northern Chile experienced very high concentrations of inorganic arsenic in drinking water , especially in the main city Antofagasta from 1958 until an arsenic removal plant was installed in 1970 .
We investigated breast cancer mortality from 1950 to 2010 among women in Region II compared to Region V , which had low arsenic water concentrations . We conducted studies on human breast cancer cell lines and compared arsenic exposure in Antofagasta with concentrations inducing apoptosis in laboratory studies .
Before 1958 , breast cancer mortality rates were similar, but in 1958–1970 the rates in Region II were half those in Region V (rate ratio RR = 0.51 , 95% CI 0.40–0.66; p < 0.0001). Women under the age of 60 experienced a 70% reduction in breast cancer mortality during 1965–1970 (RR = 0.30, 0.17–0.54; p < 0.0001) . Breast cancer cell culture studies showed apoptosis at arsenic concentrations close to those estimated to have occurred in people in Region II .
We found biologically plausible major reductions in breast cancer mortality during high exposure to inorganic arsenic in drinking water which could not be attributed to bias or confounding . We recommend clinical trial assessment of inorganic arsenic in the treatment of advanced breast cancer .
Arsenic ; Breast cancer ; Breast cancer cell line studies ; Cancer therapy ; Chile ; Drinking water ; Epidemiology .