Air Pollution and Breast Cancer: An Examination of Modification By Underlying Familial Breast Cancer Risk.

BACKGROUND

An increased familial risk of breast cancer may be due to both shared genetics and environment. Women with a breast cancer family history may have a higher prevalence of breast cancer-related gene variants and thus increased susceptibility to environmental exposures. We evaluated whether air pollutant and breast cancer associations varied by familial risk.

METHODS

Sister Study participants living in the contiguous United States at enrollment (2003-2009; N = 48,453), all of whom had at least one first-degree relative with breast cancer, were followed for breast cancer. Annual NO2 and PM2.5 concentrations were estimated at the enrollment addresses. We predicted 1-year familial breast cancer risk using the Breast and Ovarian Analysis of Disease Incidence and Carrier Estimation Algorithm (BOADICEA). Using Cox regression, we estimated HRs and 95% confidence intervals (CI) for associations between each pollutant dichotomized at the median and breast cancer with interaction terms to examine modification by BOADICEA score.

RESULTS

NO2 was associated with a higher breast cancer risk among those with BOADICEA score >90th percentile (HR, 1.28; 95% CI, 1.05-1.56) but not among those with BOADICEA score ≤90th percentile (HR, 0.98; 95% CI, 0.90-1.06; P interaction = 0.01). In contrast to NO2, associations between PM2.5 and breast cancer did not vary between individuals with BOADICEA score >90th percentile and ≤90th percentile (P interaction = 0.26).

CONCLUSIONS

Our results provide additional evidence that air pollution may be implicated in breast cancer, particularly among women with a higher familial risk.

IMPACT: Women at higher underlying breast cancer risk may benefit more from interventions to reduce exposure to NO2.