Pesticides and Breast Cancer in Hispanic Women

Institution: Public Health Institute
Investigator(s): Paul Mills, Ph.D., MPH -
Award Cycle: 2001 (Cycle VII) Grant #: 7PB-0065 Award: $299,397
Award Type: Request for Applications
Research Priorities
Etiology and Prevention>Etiology: the role of environment and lifestyle
Community Impact of Breast Cancer>Disparities: eliminating the unequal burden of breast cancer

Initial Award Abstract (2001)
Certain pesticides are extremely persistent in the environment, accumulate in fat tissue, disrupt normal hormonal functions in humans and cause cancer in laboratory animals. California is the most heavily agricultural state in the nation and millions of pounds of pesticides are applied every year. Hispanic women in California have worked as farm laborers for many generations and have had a high potential for exposure to many pesticides in the workplace and in their homes in rural areas of the state. This study is designed to determine if risk of breast cancer in Hispanic women in California is increased due to their exposure to two specific classes of pesticides commonly used on California farms today and in the past (the organochlorines and the triazines). The study will take into account factors which are already known to influence breast cancer risk such as educational attainment, social class and childbearing practices.

The primary question to be answered in this study is whether or not Hispanic women in California have increased risk of breast cancer because of their exposure to certain types of pesticides, the organochlorines and the triazines. The study will control for other factors already known to be associated with breast cancer.

Breast cancer incidence rates (which measure the occurrence of the disease in the population) will be examined for Hispanic women in each of the 58 counties of California. The amount of pesticides applied in each of the counties will also be evaluated. Statistical techniques will be used to determine if there is a correlation between the amounts of pesticides used and the breast cancer rates in Hispanic women. Also, breast cancer cases among women who have been members of the United Farm Workers of America (UFW) will be evaluated in regard to their past exposure to pesticides in the workplace. They will be compared to similar women in the UFW who have not developed breast cancer.

This study is innovative in that it utilizes data already collected by the California Cancer Registry (CCR) and the California Department of Pesticide Regulation (DPR). These data were collected with the express intent of improving the public health . Also, the study utilizes information from the membership roster of the United Farm Workers of America (UFW), a labor union which has represented thousands of poor migrant and seasonal Hispanic farm workers throughout the state of California.

Final Report (2005)
In this research we used two different approaches to evaluate the potential impact that pesticide use has on breast cancer risk in Hispanic females in California. In the first analysis, we examined the incidence rate of breast cancer in the 58 counties of California and correlated the incidence rate with county-specific use of pesticides. In order to control for known risk factors for breast cancer we simultaneously adjusted for age, socioeconomic level and fertility level in females. A total of 23,513 Latina were diagnosed with breast cancer in California during the years 1988-1999. Risk of breast cancer was positively and significantly associated with age and socioeconomic status and inversely and significantly associated with fertility levels. These finding confirm previous findings by other investigators. For some organochlorine pesticides, risk of breast cancer was positively associated with pounds of use of an insecticide, methoxychlor, such that the adjusted incidence rate ratio comparing the highest to the lowest quartiles was 1.18 (95% CI=1.03-1.35) indicating an 18% elevation in breast cancer risk in those areas with highest methoxychlor use. A similar pattern was also found for another organochlorine pesticide, toxaphene, where a risk ratio of 1.16 was found (95% CI=1.01-1.34). However, there was no association with breast cancer found with another class of pesticides, the triazine herbicides. A manuscript was prepared and submitted to Archives of Environmental Health. However, after considerable delay it was not accepted. This manuscript has been revised and submitted to the Journal of Environmental Health.

The second phase of the study evaluated breast cancer risk in women who were members of the United Farm Workers of America (UFW). In this analysis, 128 union members diagnosed with breast cancer between 1988 and 2001 were compared to 640 healthy control women and exposures to pesticides was assessed by examining work history data and pesticide use data from the California Department of Pesticide Regulation. Also we examined stage and grade of breast cancer in the farm workers in comparison to the general California Hispanic female population. Stage and grade of disease at diagnosis in farm workers was distributed approximately the same as in the California Hispanic population. Risk of breast cancer was not associated with work in any specific crops or commodities (e.g. citrus, horticulture, vegetables, grapes) except mushrooms where the adjusted odds ratios (relative risk) was 6.0 indicating a six fold elevation in breast cancer in this subgroup. After controlling for several potentially confounding variables, the risk of breast cancer associated with use of all pesticidal chemicals combined increased across quartiles of use. The relative risks increased form 1.00 to 1.30 to 1.23 to 1.41 in the highest quartile of use. Specific chemicals identified with increased breast cancer risk included chlordane, malathion and 2,4-D. Risk of breast cancer associated with chemical use was stronger in younger age women, women with early onset of breast cancer and women diagnosed earlier in the follow-up period. A manuscript was prepared and has been accepted by the International Journal of Occupational and Environmental Health.

Symposium Abstract (2003)
Risk of breast cancer in California Latina was evaluated using data from the California Cancer Registry (CCR) and the California Department of Pesticide Regulation (DPR) for the years 1988-1999. Specifically risk of breast cancer was evaluated in relationship to the number of pounds of active ingredients applied between 1970 and 1988 for two classes of pesticidal chemicals, the triazine herbicides and the organochlorines.

The CCR is a population-based cancer registry that has monitored cancer incidence and mortality in California since 1988. Data are available on a race/ ethnicity specific basis including white, non-Hispanic Hispanic, Black and Asian/Pacific Islander. Using CCR data, age adjusted incidence rates for Hispanic females (Latina) were calculated for each of the 58 counties in California for two time periods: 1988-1993 and 1994-1999. Pounds of active ingredients were also calculated for each of the 58 counties, 1970-1988. To control for risk factors for breast cancer we used an index of socioeconomic status (% of population living below the federal poverty level) and female fertility levels.

Using a negative binomial regression approach we regressed the pesticide levels on the age adjusted breast cancer incidence rates at the county level while controlling for socioeconomic status (SES) and fertility. Age, SES and fertility demonstrated the expected associations with breast cancer incidence rates in the regression models. For Latinas in the lowest quartile levels of fertility, the incidence rates ratio (IRR) for breast cancer was 1.12 (95% CI=1.01-1.24) compared to those in the highest quartile. For those Latina in the highest quartile of SES, the adjusted IRR was 1.18 (95% CI= 1.06-1.32) compared to the lowest. For most pesticides there was no significant alterations in breast cancer associated with chemical poundage in either the early of the later period. However, for two orga-nochlorine pesticides, methoxychlor and toxaphene there was evidence of a positive association especially in the earlier time period 19881993. The adjusted IRR for increasing quartiles of methoxy-chlor use were 1.00, 1.13, 1.06 and 1.18, and the IRR in the highest quartile was statistically significant. For toxaphene, the adjusted IRR in the earlier time period were 1.00, 1.09, 1.17 and 1.16 and the two highest IRR were statistically significant. None of the IRR associated with the triazine herbicides were statistically significant.

Breast Cancere Risk in Hispanic Agricultural Workers in California
Periodical:International Journal of Occupational and Environmental Health
Index Medicus: Int J Occup Environ Health
Authors: Mills PK, Yang, R
Yr: 2005 Vol: 11 Nbr: Abs: Pg:123-131

Regression analysis of pesticide use and breast cancer incidence in California Latinas
Periodical:Journal of Environmental Health
Index Medicus: J Environ Health
Authors: Mills PK, Yang R.
Yr: 2006 Vol: 68(6) Nbr: Abs: Pg:15-22