Pesticide exposure and female breast cancer risk in Canada: a case control study

Abstract

Breast cancer is one of the most common types of cancer among females in Canada. The importance of personal characteristics such as obesity, diet, age of menarche, age of menopause, parity, and family history have been implicated. However, there is only a 30% attributable risk for breast cancer from these factors. Environmental exposures are being more closely scrutinized and studies have shown that occupational and residential exposure to pesticides may be associated with increased risk for breast cancer. This thesis describes a case control study that investigated the relationship between pesticide exposure and breast cancer using data from the National Enhanced Cancer Surveillance System. All cases of female breast cancer and corresponding controls available from the data (2,360 cases and 2,488 controls) were used in the analysis. Potential pesticide exposure was assessed through self-reported lifetime occupational histories and lifetime residential histories. Known or suspected covariates were controlled for in the multiple logistic regression models. Manitoba, Saskatchewan and Alberta, the three provinces that have the highest reported usage of pesticides, were analyzed as a sub-group. Results of this study did not find any association between exposure to pesticides and an increased risk in breast cancer. However, there was a significantly negative association between women who had lived all their lives in a rural setting and breast cancer risk [odds ratio (OR) 0.70, 95% confidence interval (CI) 0.474, 0.780]. The strengths and limitations of the study are discussed. While women living in a rural setting may experience increased exposure to pesticides, women living in urban settings may be exposed to more sources of environmental toxins. Furthermore, self reported environmental exposures are difficult to measure, analyze and generalize to the larger population. Implications for future research are also included.