Organochlorine insecticides DDT and chlordane in relation to survival following breast cancer

Organochlorine insecticides have been studied extensively in relation to breast cancer incidence, and results from two meta‐analyses have been null for late‐life residues, possibly due to measurement error. Whether these compounds influence survival remains to be fully explored. We examined associations between organochlorine insecticides [p,p′‐DDT (dichlorodiphenyltrichloroethane), its primary metabolite, p,p′‐DDE, and chlordane] assessed shortly after diagnosis and survival among women with breast cancer. A population‐based sample of women diagnosed with a first primary invasive or in situ breast cancer in 1996–1997 and with available organochlorine blood measures (n = 633) were followed for vital status through 2011. After follow‐up of 5 and 15 years, we identified 55 and 189 deaths, of which 36 and 74, respectively, were breast cancer‐related. Using Cox regression models, we estimated the multivariable‐adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for lipid‐adjusted organochlorine concentrations with all‐cause and breast cancer‐specific mortality. At 5 years after diagnosis, the highest tertile of DDT concentration was associated with all‐cause (HR = 2.19; 95% CI: 1.02, 4.67) and breast cancer‐specific (HR = 2.72; 95% CI: 1.04, 7.13) mortality. At 15 years, middle tertile concentrations of DDT (HR = 1.42; 95% CI 0.99, 2.06) and chlordane (HR = 1.42; 95% CI: 0.94, 2.12) were modestly associated with all‐cause and breast cancer‐specific mortality. Third tertile DDE concentrations were inversely associated with 15‐year all‐cause mortality (HR = 0.66; 95% CI: 0.44, 0.99). This is the first population‐based study in the United States to show that DDT may adversely impact survival following breast cancer diagnosis. Further studies are warranted given the high breast cancer burden and the ubiquity of these chemicals.