Etiology & Prevention: Finding the Causes & Ending the Danger
Community Research Collaboration – Full Research Awards
Request for Applications (RFA) Awards
Innovative, Exploratory and Developmental Awards – Type I
Innovative, Exploratory and Developmental Awards – Type II
A life lived without fear of disease is a hope of mankind that has taken many forms over the centuries. Despite enormous gains in the last fifty years in our understanding of the physiology of health and disease however, cancer 'prevention' means reducing the risk of getting cancer. For some cancers, the reduction in risk by the alteration of lifestyle can be quite dramatic, since we have identified strong etiologic (causal) factors: smoking for lung cancer, and smoking, chewing tobacco, and alcohol (alone or in combination) for oral cancers as examples.
For breast cancer, there are as yet no comparable lifestyle alterations to effect a dramatic decrease in risk. Very recently, tamoxifen prophylaxis has been shown to reduce risk (in postmenopausal women only), but there are a number of conditions which preclude its use, and it can have serious side effects.
However, even with tamoxifen, the concept of risk reduction applies properly to a population. That is, an individual cannot be sure that not smoking means that she will not get lung cancer, that staying very thin after menopause or taking tamoxifen means that she will not get breast cancer, even though for the U.S. population as a whole, staying thin after menopause seems to be associated with a slightly lower rate of breast cancer overall, and the lung cancer rate for non-smokers is dramatically lower than that of smokers, for example.
The goal of most of the work that BCRP funds that looks at risk and risk reduction is now aimed at understanding the individual differences in women who contract breast cancer and those who do not, even though they are similar in many other respects such as lifestyle and family history. Why is it, exactly, that among identical twins raised together, for example, one twin will get breast cancer, and the other not? This search for underlying causes is now carried on at the genetic level, either through use of human tissue, laboratory animals, or cell cultures, thereby linking etiology and prevention very closely together.
Given the evidence that there is a strong association between lifetime exposure to estrogen and increasing breast cancer risk, it is not surprising that six of the eight grants funded under this priority issue are aimed at understanding the role of estrogen, though their approaches differ widely. Leslie Bernstein will investigate leptin, a newly discovered hormone produced by fat cells. Large amounts of adipose (fat) tissue in obese women increase circulating estrone (a form of estrogen) levels in proportion to the amount of adipose tissue. Leptin could be a factor in breast cancer etiology because of the important role that it plays in fat storage and metabolism. Donna-Williams Hill will undertake to isolate the mechanisms by which exercise produces protective factor(s) against breast cancer. Many studies have been conducted, but it is not yet known what types, duration, intensity of exercise is likely to be best and for whom. By using a rat mammary model, Dr. Hill will be able to control for several of the factors (confounding variables) which to date have made interpretation of exercise studies in humans difficult. Brian Henderson will look at several molecules, called insulin-like growth factors or IGFs, that collaborate in stimulating cell division by mediating the effect of estrogen. He will analyze blood samples from postmenopausal African-American, Japanese, Latina, and non-Latina White women to determine if circulating levels of IGFs and their binding proteins differ by race or ethnicity. His results will enlarge those of a previous study by a colleague showing strong positive association between IGF-1 and breast cancer in a small group of premenopausal White women. Vicki Davis will investigate whether it is possible to obtain protective effects against breast cancer by inhibiting estrogen action in the breast, while maintaining the important beneficial effects of estrogen such as protecting against heart disease and osteoporosis, by looking closely at a natural variant of the estrogen receptor on cells called estrogen receptor alpha.
There is strong evidence that certain dietary patterns are associated with lower breast cancer risk. Most notable of these is a diet rich in soy products which seems to lessen the impact of estrogen on breast cells. Anna H. Wu will conduct a case-control study to investigate soy-estrogen metabolizing gene interaction, specifically variants of the CYP17 and COMT genes. This large study (which will result in a sample size of approximately 1300 cancer cases) is necessary to sort out the complex and interrelated lifestyle/environmental and genetic factors in breast cancer development.
Ann Hamilton will probe the genetic basis of estrogen's role in breast cancer from yet another direction by looking at pairs of identical twins. Using tissue from 200 pairs of identical twins, both with breast cancer, 200 pairs, one with breast cancer, and 100 pairs, neither with breast cancer, she will compare the frequency of one genetic polymorphism among these groups, called the A2 allele on the CYP 17 gene, which has been shown to be related to higher levels of estrogen.
Two studies undertake other etiologic investigations: adolescent risk factor identification, and testing hypotheses about a mechanism by which cell growth may become uncontrolled. Georgianna Farren and Margaret Wrensch (co-PIs), heading a community-university collaboration, will investigate possible risk factors encountered by adult women residents of Marin County during their adolescence. An important methodological innovation is the development of survey instruments that may prove very useful in overcoming one of the most intractable barriers to such research, namely the accuracy and completeness of recall by women of events which occurred decades previously. Another study will investigate the role of the enzyme ornithine decarboxylase. Based on previous research, it appears that ornithine decarboxylase exists in rapidly growing and cancerous tissue at high levels. Craig Byus will attempt to identify in model cell lines of human mammary tissue and carcinomas where there are genes that are turned on and off when ornithine decarboxylase is present at these high levels, as a preparatory step to understanding their function.
Community Research Collaboration- Full Research Award
Marin County Breast Cancer Study of Adolescent Risk Factors
Georgianna Farren, M.D.1, and Margaret R. Wrensch, Ph.D.2
1Marin Breast Cancer Watch and the 2University of California, San Francisco
The purpose of this study is to examine the potential relationships among established breast cancer risk factors and understudied or novel adolescent and pre-adolescent risk factors in Marin County, California. The study is a collaboration between Marin Breast Cancer Watch (MBCW) and the University of California, San Francisco. The long range goal of MBCW is to discover risk factors that ultimately may lead to a reduction of breast cancer incidence.
MBCW is a grass-roots, nonprofit, tax-exempt organization of approximately 350 members, established in 1995 because of community concern regarding the extremely high incidence (133.2 per 100,000 for the 1900-94 period) of breast cancer in Marin County. With the University of California, San Francisco, we conducted a BCRP-funded pilot study to determine the feasibility of conducting a large study with a traditional research partner and to assess the need for a larger study.
We reviewed the pertinent literature and developed a questionnaire and memory tools to overcome the difficult problems of recalling distant past life events. We also conducted focus groups and interviews with Marin County residents with and without breast cancer to evaluate and will pretest the memory tools and the questionnaire.
Guided by the results of the pilot study, we will conduct a large study in Marin County of relatively unexplored adolescent as well as known breast cancer risk factors. Our major question is: did adolescent and pre-adolescent experiences significantly differ between women with and without breast cancer in Marin County? Specific factors to be compared are: (1) physical development and changes; (2) adolescent stress, family and social connections; (3) detailed adolescent and contemporary socioeconomic factors; (4) passive and active smoking; (5) alcohol use; (6) residency and migration and (7) known breast cancer risk factors.
Few readily modifiable risk factors for breast cancer have yet been defined, despite studies showing that breast cancer risk is modifiable over a single lifetime. Adolescent factors have been understudied. This study will address two priority areas of breast cancer research, namely, breast cancer etiology, through greater attention to relatively unexplored adolescent and pre-adolescent factors, and prevention, through inclusion of some potentially modifiable behavioral and psychosocial factors.
Specifically, we will conduct in-person interviews with 300 women with breast cancer diagnosed between Septemebr 1, 1997 and June 30, 1999 in Marin County identified through the local cancer registry and 300 appropriately matched controls from the same population. We will evaluate four primary hypotheses about: (a) ages at menarche and breast development; (b) major life events before age 21; (c) adolescent and/or adult socioeconomic status; (d) age-adjusted lifetime years residing in Marin County. We also will evaluate associations of other adolescent social and lifestyle factors with breast cancer; write articles for scientific journals about our pilot and full study results; conduct community educational forums; and develop newsletter items and a website.
We expect that by increasing knowledge of breast cancer etiology, our studies ultimately will enhance possibilities for breast cancer prevention. Specific to the problem of high breast cancer rates in Marin County, finding no differences in cases and controls for total years of residence in Marin County might allay community concerns about Marin specific environmental exposures, while finding a difference might generate enthusiasm for additional explanatory studies. Bringing together community members and scientists in this successful collaboration may encourage other communities to take an active role in cancer research. Most importantly, information obtained may suggest learning tools and lifestyle changes in adolescence that can be incorporated into the lives of our daughters to prevent breast cancer.
Request for Applications (RFA) Award
Estrogen-metabolizing Genes, Soy and Breast Cancer in Asians
Anna H. Wu, Ph.D.
University of Southern California; Department of Preventive Medicine
There exists indisputable evidence showing a positive association between increasing total lifetime exposure to estrogens and increasing breast cancer risk. The identification of modifiable lifestyle factors that could reduce lifetime estrogen exposure and thus the risk of breast cancer is a research priority. Preliminary analysis of a study funded by the BCRP in 1995 ("A Case-Control Study of Breast Cancer in Asian-Americans") showed very promising results that high intake of soy foods is associated with a 30% reduction in risk of breast cancer. There is compelling reason to expand this study, in order to address the relationship of soy in breast cancer development in a comprehensive manner that includes the investigation of estrogen metabolizing genes suspected of influencing breast cancer risk, and possible gene-diet interactions in disease risk. A sufficiently large study is critical if one hopes to sort out the complex and interrelated lifestyle/environmental and genetic factors in breast cancer development.
This project is aimed at expanding the ongoing case-control study to include candidate estrogen metabolizing genes that may interact with soy in affecting breast cancer development. This added goal of investigating soy-gene interaction in breast cancer necessitates interviewing and collecting blood specimens from an additional 780 Asian women with breast cancer and an equal number of population controls. This combined sample size of 1300 cases and an equal number of controls (520 breast cancer cases and 520 controls will have been interviewed by the end of the current BCRP grants, will allow us to determine if risk of breast cancer is increased: 1) in the presence of the high activity A2 allele of the CYP17 gene, and 2) in the presence of the low activity Met allele of the COMT gene. We also will determine if there is gene (CYP17)-gene (COMT) interaction as a risk factor for breast cancer, and if there is gene (CYP17 and/or COMT)-diet (soy) interaction in the causation of female breast cancer.
Innovative, Exploratory and Developmental Awards – Type I
Postmenopausal Breast Cancer: Obesity and the Leptin Receptor Gene
Leslie Bernstein, Ph.D.
University Southern California; Norris Comprehensive Cancer Center
Women who are obese at or after the time of menopause have a greater chance of developing breast cancer than women who are thinner. This may be due to higher levels of estrogen resulting from the obesity. (Obesity is defined as meaning over 30 on the Body Mass Index, BMI, which is a measure based on weight and height.) Leptin, a newly discovered hormone produced by fat cells, may also be related to breast cancer because leptin levels are related to several hormones thought to be associated with breast cancer. The proportion of women who are obese is increasing dramatically, particularly among women who have the greatest risk of breast cancer, those over the age of 50. Therefore, it is critical to gain a better understanding of factors that contribute to the development of obesity and how obesity increases breast cancer risk.
This pilot study will determine women's body fat distribution by several methods, will measure several hormones in blood including leptin, and will identify what type of leptin receptor gene (OB-R) the women have. The leptin receptor gene is related to the body's response to leptin; obese women do not respond to leptin, and we think the (OB-R) gene may be related to breast cancer because it appears to be related to obesity. In the pilot study, we will look at the relationships between different kinds of obesity, hormones in blood and different types of the leptin receptor gene (OB-R). Our overall objectives are to establish baseline measurements and then develop a more definitive study of the relationship between subtypes of obesity, OB-R and breast cancer risk as well as an experimental study of how exercise affects changes in body fat and hormones in women with specific types of obesity.
We propose to study healthy obese postmenopausal African-American and Caucasian women who are 50 years of age or older (n=100) and who previously participated in our study of breast cancer risk factors. We already have extensive information from these women about their family history of cancers, use of oral contraceptives and other hormones, reproductive histories, and lifetime exercise history. We will ask new questions about their current medical history, family histories of diabetes and obesity, current exercise patterns, current medication usage, and diet.
Participants will be invited to our physical therapy laboratory where they will complete the study questionnaire, and where we will measure their body fat distribution, and draw a blood sample that will be used to measure hormones and the OB-R gene. We will use several different methods to measure body fat including measuring skinfold thickness, calculating the waist-to-hip ratio, calculating body-mass-index based on weight and height, and DEXA scanning, a non-invasive means of measuring percent body fat.
Certain types of obesity (upper body vs. lower body) may reflect hormone levels and variations of the OB-R gene that are associated with a greater chance of developing breast cancer than others. This study will generate new information about the relationship between obesity and hormones with respect to this gene and enable us to ask more refined and specific questions about what causes breast cancer in the future and enable us to develop more focused programs for risk reduction.
Breast Cancer Susceptibility Genes in Very High Risk Women
Ann S. Hamilton, Ph.D.
University of Southern California
A woman with relatives who have had breast cancer has a higher risk of developing the disease than a woman who does not have relatives with the disease. However, within identical twin pairs, the twin of a breast cancer case has an even higher risk of developing the disease than other women with a family history of breast cancer. We have developed a large twin registry and have identified nearly 1200 identical twin pairs in which one twin has had breast cancer and 276 pairs in which both twins have had breast cancer. Twins in the registry completed a questionnaire when they first volunteered to be part of the registry. We have studied the responses within pairs where both had breast cancer and we found that some well known risk factors for breast cancer, especially those related to earlier development and onset of menstruation, were strongly related to the twin who developed breast cancer first in the pair. Since these women are at a high genetic risk of disease, we want to test our hypothesis that genetic factors related to estrogen metabolism may occur more often in these pairs than in others where breast cancer is not as common.
To test our hypothesis we need to obtain DNA from tissue blocks that were preserved when the breast cancer was first diagnosed and treated. In an earlier study we have begun to obtain these blocks and will complete the process with this study. In total, we will obtain tissue from 200 pairs of identical twins where both have breast cancer, 200 pairs where one has breast cancer, and 100 pairs in which neither have had breast cancer. We will compare the frequency of one genetic polymorphism (called the A2 allele on the CYP 17 gene) among these groups. This genetic polymorphism has been shown to be related to higher levels of estrogen in some women. We want to determine if this genetic factor occurs more often in the pairs where both have breast cancer than in the other pairs.
This study is very important because not much is known about specific genetic factors related to breast cancer, other than the widely publicized BRCA1/2 genes. While those genes carry a high risk of developing breast cancer, they are not very common in the population and do not account for all of the cases who have reported having a family history of the disease. We know that young women with breast cancer are more likely to have a genetic factor related to the development of their disease; however, the actual number of cases caused by genetic factors is much greater among those diagnosed after menopause, because breast cancer is so much more common then. The genes responsible for this late disease are not known, but are more difficult to identify because only a small proportion of those with the gene get the cancer, presumably because other factors are required. The twins in this study represent a high genetic risk group and the estrogen related risk factors that we have seen are especially strong in the older twins. Thus the study can contribute important knowledge to identifying the additional genetic factors related to breast cancer.
Exercise, Hormones and Breast Cancer Prevention
Donna Williams-Hill, Ph.D.
University of Southern California School of Medicine
Studies on humans and in the laboratory suggest that breast cancer risk is lower in individuals who exercise on a regular basis. The results have been inconsistent, however, with some studies showing a reduction and others showing no effect or an increase in breast cancer occurrence. Thus, the conclusions reached by these investigations must be viewed with a degree of caution. The differences reported in part are due to the variation in exercise programs investigated in terms of how long one exercises, the type of exercise performed and the amount of effort one has to put into that particular form of exercise. Other factors to consider in humans are one's inherited breast cancer susceptibility, variations in diet and other life style complications.
In this study we intend to study the effect of exercise on breast cancer using a rat mammary model. These experiments will control for several of the confounding variables present when trying to conduct similar studies on humans. All animals will be exercised for the same periods of time in the same way. We will study animals as they develop through puberty, become pregnant and nurse their offspring to determine if the effect of exercise is preventive when the hormonal status of a female is changed. We will also apply the same exercise regime to females whose ovaries have been removed to simulate the menopausal state and in females where the ovaries have been removed but estrogen replaced to simulate estrogen replacement therapy in females. In addition, we will investigate the role of a single nutritional supplement, vitamin E, in the prevention of mammary cancer.
For the human female, questions such as how much exercise and what type of activity is required for this protection are key. At what age should exercise begin to be of benefit? We also would like to know if women carrying a genetic predisposition to breast cancer can benefit from exercise. To that end, we have chosen a rat strain that is genetically susceptible to mammary cancer for these studies. The ultimate goal of these experiments is to contribute to the understanding of the link between exercise and breast cancer prevention so that public education programs and health policies can be developed to address this important issue.
Innovative, Exploratory and Developmental Awards – Type II
Unique Genes Expressed in Cancer Cells
Craig V. Byus, Ph.D.
University of California, Riverside
All cells and tissues contain small highly-charged chemicals called polyamines. These polyamines are required for the growth and differentiation of all cells and tissues. A single enzyme present in all cells and tissues catalyzes the synthesis of these polyamines. For many years, we have known that these polyamines and the enzyme ornithine decarboxylase (ODC) exist in rapidly-growing and cancerous tissue at high levels. Furthermore, investigators have shown that if you use a specific chemical or drug that inhibits or blocks polyamine biosynthesis (DFMO), a marked reduction in the growth of the cell or tissue can be observed. It also was apparent that the high degree of regulation which occurs in "normal" cells and tissues of the polyamine biosynthetic pathway was somehow abnormal or unregulated when cells and tissues became transformed into cancer cells. It now appears that the enzyme ODC itself may function as a cancer-causing (oncogenic) protein when there is enough of the enzyme present inside of the cell.
Using a variety of molecular biological techniques, it is now possible to engineer cells which have artificially high levels of ODC and polyamines and to examine what stable high levels of ODC expression does to the cancer-related properties of these cells. In this regard, ODC overexpression results in a cell which is more cancer-like in nature and is able to grow without the kind of supporting matrix that normal cells require, will form tumors when injected back into an animal, and in many cases, the tumors formed are more highly invasive (malignant) and more highly vascularized, i.e., have higher blood supply to them. It is our hypothesis that these cells overexpressing ODC have a different group of genes that are now turned on and off. The specific genes which are turned on or off following high levels of ODC, are what allow the cell to become more cancer like.
We intend to identify in model cell lines of human breast tissue and carcinomas where there are genes that are turned on and off when ODC is overexpressed. It is our hope that once these genes are discovered and their function is understood, we will be much closer to understanding the process by which normal breast tissue becomes cancerous.
Breast Cancer Prevention by a Dominant Negative ER Variant
Vicki Davis, Ph.D.
Cedars-Sinai Medical Center
Breast cancer is a highly prevalent disease that destroys the lives of women from their reproductive years through postmenopausal ages. Tamoxifen therapy, which was shown in a recent study to lessen the risk of breast cancer, reduces estrogen activity in the breast. However, this therapy also modifies the ability of other tissues to respond to estrogen, tissues which benefit from estrogen action, causing adverse effects on reproduction, cardiovascular fitness, menopausal symptoms, and uterine cancer risk. Therefore, to circumvent these problems, we will test a novel means of breast cancer prevention that inhibits estrogen action in the breast, but not in other tissues that benefit from the actions of this hormone.
In the breast and other tissues that respond to estrogens, estrogen acts by interacting with a protein known as the estrogen receptor. The presence of this receptor in breast cancer is used by physicians to determine treatment strategies for the patient. Our design involves interfering with the normal actions of the estrogen receptor in order to modify the tissue's ability to respond to estrogen. As shown with tamoxifen, interfering with estrogen's ability to stimulate the growth of breast cells can reduce the risk of breast cancer. In this study, we propose to investigate the ability to inhibit estrogen receptor action, in the presence of estrogen, to prevent breast cancer in mice. These mice develop mammary cancer that frequently spreads to the lungs. We will determine whether the mice remain tumor-free for longer periods and if the number of tumors that develop and that invade the lung are reduced in mice that have the modified receptor compared to mice that do not, as is suggested by our preliminary results.
Demonstrating in our mouse model that estrogen action can be suppressed in the breast in the presence of estrogen would provide the evidence to guide the development of new breast cancer prevention therapies for pre- and post-menopausal women. By devising a therapy that can simultaneously protect organs that need estrogen and protect the breast from estrogen, the benefits to women's health and life span would be immense. Development of this novel method to defeat estrogen effects on breast cancer would substantially reduce the impact of the disease without adversely affecting mammary gland function. In addition, the benefits would include an improved quality of life, especially for women in their reproductive years or at high risk for other life threatening diseases associated with loss of estrogen, such as osteoporosis and heart disease.
IGF System and Breast Cancer in Postmenopausal Women
Brian Henderson, M.D.
University of Southern California
The sex hormone estrogen most likely plays a crucial role in breast cancer development by making cells in the breast divide faster and thus have an increased likelihood to become cancerous. On the molecular level, insulin-like growth factors (IGF) are believed to be one of the mediators of the estrogenic effect. The insulin-like growth factor system consists of several molecules that collaborate in stimulating cell division. In fact, laboratory and animals studies indicate that the insulin-like growth factor system is involved in causing breast cancer. For example, animals that were genetically altered so that their IGF-system has an increased activity have a higher likelihood of developing breast cancer.
Human data on the association between the IGF-system and breast cancer is more limited and restricted to non-Latina white women. One large study, though, found that premenopausal women with high IGF-1 levels in their blood have a higher risk of developing breast cancer than women with low IGF-1 levels. In the future, this association must be confirmed in different ethnic groups and for postmenopausal women. We plan, therefore, investigations in a multiethnic population of African-American, Latina, Japanese, and non--Latina white women (breast cancer cases and controls). We plan to investigate whether ethnic differences exist in the activity of the IGF-system activity according to ethnic differences in breast cancer risk, and we plan to investigate whether mutations in two genes of the IGF-system are related to breast cancer risk in different ethnic groups. Biological material for this study population is already available.
The potential of our study lies in several areas: First, the study has the potential to improve our understanding of breast cancer etiology. Second, the study has the potential to identify new targets for breast cancer prevention and therapy. The IGF-system may for example provide us with breast cancer susceptibility markers that help to better target women for mammography screening. Third, the study makes use of material already collected from a multiethnic study population.
