Authors
C. Hopenhayn-rich, M. L.Stump, S. R. Browning

Title
Regional assessment of Atrazine exposure and incidence of breast and ovarian cancers in Kentucky

Journal
Archives of environmental contamination and toxicology. 2001; 42:127-136

Summary
The hormone-dependency of most ovarian, breast and endometrial cancers has led to the hypothesis that exogenous estrogenic compounds in the environment could be contributing factors in the etiology of these cancers. There have been a number of reports in the literature that have examined the association between exposure to atrazine and various cancers. Atrazine is an organochlorine compound, has been widely used as a herbicide in the United State for at least 40 years, mainly in corn production, and it is currently the most commonly used herbicide. With 68-73 million pounds of active ingredient applied in 1995, atrazine is the predominant herbicide used on a pounds applied basis. This study is an expansion of an ecologic study of breast cancer in Kentucky (Kettles et al. 1997), investigating the relationship between several indices of atrazine exposure to ovarian and breast cancer over a 5-year period (1993-1997). Counties were grouped into 15 Area Development Districts (ADDs). The ovarian and breast cancer age-adjusted incidence rates were obtained from the Kentucky Cancer Registry (KCR). For this study, authors assumed that the main route of Atrazine exposure to the general population was through drinking water. However, due to the limitations in drinking water data, authors used three sources of data to derive atrazine exposure indices: public drinking water atrazine levels, acreage of corn planted, and atrazine sales in Kentucky.

Atrazine levels in drinking water were weakly and inversely associated with breast and ovarian cancer. In the univariate analysis, authors did not find an indication of an association or a trend between the atrazine exposure scores and breast cancer incidence. On the other hand, the analysis by county showed a decreasing trend in ovarian cancer risk with increasing exposure, across each of the three individual indices (atrazine in water, atrazine sales, and acres of corn planted). This association was statistically significant and strongest for corn. The inverse association between the total exposure estimate and the corn score with ovarian cancer incidence may be due to certain lifestyle or reproductive factors that are differentially distributed among rural women and influence the risk of ovarian cancer (e.g. have an earlier age at first birth, higher mean number of births, older age at menarche, and younger age at menopause). The following are the rate ratios (RR) and corresponding 95% confidence intervals, using the lowest quartile as base line (RR= 1.0), and the county as the unit of analysis: 1.01 (0.83-1.21), 0.77 (0.66-0.90), and 0.76 (0.65-0.88). A null association was found for breast cancer across all exposure indices, both by county and by ADD. Although, for breast cancer, the only positive association was observed in the highest corn quartile.

Although not the topic of this study, it has been hypothesized that different types of ovarian cancer may have different etiologies. In particular, investigators have postulated that exogenous estrogenic compounds may only increase the risk of nonmucinous ovarian tumors. In this study, when authors stratified the data the proportion of nonmucinous tumors was found by ADD ranged from 76-92%. It is noteworthy that the highest percent of nonmucinous ovarian cancers were found among the highest atrazine-exposed ADDs. Due to the inherent limitations of this type of study it is possible that other factors such as diet, and exposure to other chemicals both from the environment or through intentional consumption may be contributing to these findings. Studies using individual-level data are recommended to elucidate the relationships between estrogenic environmental exposures and female reproductive cancers.