Internal Chemical Exposure Study among Mexican Immigrants

Investigator: Laura Fejerman, PhD
Sponsor: California Breast Cancer Research Program

Location(s): United States


Non-technical overview of the research topic and relevance to breast cancer: Breast cancer risk increases with number of generations in the U.S. and with younger age at migration among U.S. Latinas. These observations strongly suggest that the changes in the environment and lifestyle associated with longer residence in the U.S., increase Latina women’s exposure to harmful factors and as a result increase their breast cancer risk. Previous studies have attempted to identify the factors that could explain the differences in breast cancer risk among Latina immigrants using measures of exposure obtained through questionnaires. However most of these studies are limited to epidemiological associations without further insights into underlying mechanisms. It is known that people with similar reported exposures are not equally susceptible to disease, probably due to variation in the way substances produced within or outside our bodies are broken down and handled by our organisms. There is a need for new studies that objectively assess internal levels of exposure among U.S. immigrants. Our study will assess how the migratory experience influences the levels of potentially harmful substances present in the blood of Mexican Americans women increasing their risk of developing breast cancer.

The question(s) or central hypotheses of the research: We hypothesize that women who have been exposed to the U.S. environment and lifestyle for longer and from a younger age, will have higher levels of harmful substances in their blood. We also hypothesize that particular types of harmful compounds will measure at different levels depending on duration of residence in the U.S. and age at migration as well as when comparing breast cancer cases and controls.

The general methodology: We will measure multiple chemical exposures that are detectable within the body of any given individual without targeting any one in particular. Similar to the shift from candidate gene studies to genome-wide association studies (GWAS) in investigations of the genetic etiology of diseases, our project proposes a shift from breast cancer candidate exposure analysis to an exposure-wide analysis. We plan to use mass- spectrometry (a substance separation procedure) and cell-based assays to measure two types of harmful substances: reactive electrophiles (substances attracted to electrons that damage DNA and proteins) and hormone receptor disruptors (chemicals that mimic the effect of estrogen or androgen on cell receptors). We will evaluate the levels of these two compounds among 90 Mexican American women who participated in the San Francisco Bay Area Breast Cancer Study (SFBCS), a population-based case-control study of women aged 35 to 79 years. We will compare levels of 30 women born in the U.S., 30 born in Mexico who moved to the U.S. before puberty (as marked by first menstrual cycle), and 30 who moved to the U.S. as adults (at age 21 years or older). Each migration group will include equal numbers of pre- and post-menopausal women. Through linkage with the California Cancer Registry, we expect to identify approximately 30 women who developed breast cancer since they participated in the study. We will contrast the reactive electrophile levels and hormone receptor disruptor activity of these cases to those of women who have not yet developed the disease.

Innovative elements of the project: The innovation in this proposal comes from the idea of combining information on migration history with untargeted measures of internal exposure to harmful substances among Mexican Americans. By avoiding a priori assumptions about what specific chemicals are likely to affect breast cancer risk, we expect to open new avenues of research and discover new biological markers of risk (or biomarkers) as well as new modifiable risk factors that could be targeted through prevention programs to reduce breast cancer incidence among higher generation Latinas.