Prevention
Prevention of breast cancer was assigned as a high priority research area by the Breast Cancer Research Council. Since human clinical cancer prevention trials require large amounts of money and large numbers of subjects to achieve meaningful results (usually requiring nationwide collaborations), the Council chose to focus on funding innovative, targeted, research proposals that, if promising, could be carried forth at another level and serve as examples nationwide. Consideration was given to the possible scope of prevention research, and research aimed at the following areas was chosen: (1) identifying and eliminating or modifying causative agents; (2) methods to detect women at highest risk, in order to identify those who would most benefit from preventive interventions; (3) development of new biologics (e.g. cytokines, antibodies, vaccines, enzymes) and natural compounds (e.g., phytoestrogens) that might serve as preventive therapies; and (4) characterization of novel cellular mechanisms (e.g., integrins, growth factors and their receptors, telomerase) to be targeted by potential preventive agents.
Five grants in the first three categories were funded.
In the first category, one study will examine the damage to breast cells
caused by certain metals, and the potential mediating effect of selenium
on this process. In the second category, two studies are examining the potential
of the appearance of the breast on mammograms, with or without the addition
of examination of nipple fluid, to be used to identify women at highest
risk of breast cancer. One of these studies focuses on African American,
Hispanic, and Asian women. Two studies are included in the third category.
One is examining the potential of a new preventive agent to improve on the
currently-used drug, Tamoxifen, by avoiding the serious effects of endometrial,
and possibly liver, cancer. The other study uses computer-aided drug design
and laboratory synthesis to develop agents based on the potential cancer-preventing
element found in green tea. Abstracts in the last category are included
in the "Pathogenesis" section, since these two categories overlap.
These more basic studies are likely to result in new potential preventive
agents which will be seen in this section in future Cycles.
Research Project Awards
- Molecular Control of Breast Exposure to Selenium
- Mammogram Density, Nipple Aspirate Fluid & Breast Cancer Risk
- Mammographic Densities and Breast Cancer Prevention
Molecular Control of Breast Exposure to Selenium
Stephen Howell, M.D.
University of California, San Diego
It is the overall goal of this research to reduce the damage done by cancer-causing metals to breast cells. Cadmium, arsenite, and nickel ions can cause cancer, and along with lead are important industrial toxins to which women are exposed via dietary and environmental contamination. Selenium can offset the cancer-causing effects of cadmium, arsenite, and nickel, and reduce the toxicity of lead. Deficiency of this micronutrient has been reported to be a risk factor for the development of breast cancer. We have isolated a previously unknown human gene (hARSA-I) whose expression can influence the sensitivity of the cells to selenite (the salt form of selenium), arsenite, cadmium, and nickel. The protein product of the hARSA-I gene is part of a membrane transporter (abbreviated HART) that appears to play a central role in the ability of these metals to get into and out of cells. It is our hypothesis that HART is a major determinant of the effect of selenium and cancer-causing metals in breast cells, and plays a role in mediating the ability of selenium to offset the toxic effects of arsenite, cadmium, and nickel.
The specific aims of this study are to: (1) determine whether an increase in the expression of the hARSA-I gene alters uptake of selenium in normal human breast cells. The effect of increased hARSA-I gene expression on initial uptake, content at steady-state, efflux, location within the cell and toxicity will be compared in pairs of normal breast cell populations that differ only in the extent of hARSA-I expression. (2) determine whether either prior exposure or concurrent treatment of breast cells with selenite can alter the expression of hARSA-I, or the activity of the HART pump, and whether such changes alter the uptake and efflux of selenium; and (3) determine the pattern of expression of the hARSA-I protein in normal human breast tissue samples by immunologic staining, and whether the pattern or level of expression differs in benign or fully malignant lesions of the breast. We have produced an antibody to hARSA and demonstrated that it can be used for such immunologic staining studies.
The discovery of the hARSA-I-related transporter (HART) provides a novel way to address fundamental questions about the role of selenium and related micronutrients in the chemoprevention of breast cancer, and to develop rational dietary and hormonal strategies for reducing breast cancer risk.
Mammogram Density, Nipple Aspirate Fluid & Breast Cancer Risk
Nicholas Petrakis, M.D.
University of California, San Francisco
Mammography has long been established as the leading method for the early detection of breast cancer. In addition to its value for the diagnosis of cancer, investigators have found that certain non-cancerous breast changes that appear in the mammogram may be indicators of increased future risk of breast cancer. Recently, several studies have shown that the amount of dense areas seen on mammograms ('mammographic density') is a sign of increased risk of breast cancer. These areas of density indicate the amount of glandular and connective tissue (as opposed to fat, which is the third type of tissue in the breast) within the breast. Two recent large-scale studies found that risk of breast cancer is increased in proportion to the amount of dense areas in mammograms. It was found that women with areas of mammographic density occupying more than 75% of the mammogram had a four- to five-fold increased risk of breast cancer compared to women with area of density occupying less than 10% of the mammogram. The risk increased in proportion to the amount of the breast occupied by areas of density. This increased risk has persisted throughout the period for which data is available for these women, which at present is 5 to 10 years after the mammogram. (Using other funds, the breast cancer risk of these women will continue to be assessed at appropriate intervals.)
Our group has pioneered the use of nipple aspirates of breast fluid for epidemiologic studies of the changes in the structure and function of breast cells and the biochemistry of the breast. Nipple aspiration employs a breast pump to obtain small amounts of fluid which can be employed as a kind of a "Pap smear' for study of breast disease, cancer, and precancerous conditions. Between 1975 and 1980, we obtained nipple aspirate fluid (NAF) from 2,162 women who underwent mammography at the Breast Screening Center of Northern California at Merritt Hospital, Oakland. We found that women whose NAFs contained unusual or "atypical" breast epithelial cells had a five-fold increased risk of breast cancer compared to women who did not yield any breast fluid. Among premenopausal women with atypical cells, the risk was increased 15-fold over non-yielders of NAF. This higher risk has held true, persisting for the 10- to 18-year period for which breast cancer statistics are available. (The breast cancer risk of these women will likewise continue to be assessed as data becomes available.)
The purpose of this study is to determine if the combination of mammography and NAF analysis improves our ability to estimate a woman's risk of developing breast cancer. Our study will use data already collected, including age, race, breast cancer risk factors, NAF cytology and, in addition, current breast cancer status as of December 1995. However, it will be necessary for the radiologists to re-measure all 2,162 mammograms for area of mammographic density before carrying out the epidemiological and statistical analyses. The fact that the status of all the women is currently known will make it possible to determine the extent to which the prediction of breast cancer risk is enhanced by the combination of area of mammographic density and cytologic diagnosis.
If combining the methods of area of mammographic density and nipple aspiration cytology is found to significantly improve the prediction of women at risk above either method alone, this approach could be used to separate women at highest risk from those at lowest risk, and would be of particular usefulness in premenopausal women with dense breasts, and women with a family history of breast cancer, or a prior benign biopsy. This information would be useful for recruitment of subjects for preventive trials, for women undergoing genetic counseling, and for targeting preventive interventions.
Mammographic Densities and Breast Cancer Prevention
Malcolm Pike, Ph.D.
University of Southern California
It is well known that mammograms have been found to be useful in identifying early existing breast cancers before they can be felt. Less well known is that mammograms taken in a woman without breast cancer may also be used to convey very useful information as to the woman's future risk of breast cancer. The appearance of the breast in mammograms is determined by the relative amounts of fat, connective tissue, and epithelial tissue. (Breast epithelial tissue is the tissue in which the majority of breast cancer arises.) On mammograms, fat appears as radiologically lucent (clear) areas, whereas connective and epithelial tissue appears slightly darker, resulting in mammographic "densities." Higher levels of mamographic densities have been found to be strongly predictive of breast cancer risk in certain groups of (non-Latina) White women. We propose to study whether mammographic densities can be used to predict the risk of breast cancer in African-American and Asian-American as well as in White (Latina) women, and in younger as well as in older women. We will also study whether the known ethnic differences in breast cancer risk will be reflected in differences in mammographic densities across these ethnic groups. In addition, we will study whether the protective effects of physical exercise on breast cancer risk is reflected in reduced mammographic densities.
The proposed study represents an addition to two ongoing studies in our department, the Los Angeles part of the nationwide Women's CARE study, and a study of breast cancer in Asian Americans. We will determine the extent of mammographic densities in 240 African-American, 240 White, and 150 Asian-American breast cancer cases, and an equal number of African-American, White and Asian-American controls (women without cancer).
If mammographic densities can be shown to provide consistent, wide-ranging predictive power regarding breast cancer risk, and to reflect differences in major breast cancer risk factors, they then could be used to indicate degrees of risk for breast cancer. This could be added to information about other known risk factors, such as family history, being a carrier of certain mutant genes, etc. to help estimate a woman's risk of breast cancer. Indeed, they could be used instead of these and other, as yet unknown, risk factors to provide a more precise measure of risk. Such a "surrogate" measure of risk would be of great value in genetic and other risk factor reduction counseling, and in public health breast cancer prevention efforts, by enabling high-risk target populations to be defined.
New Investigator Award
Analogs of Tea Polyphenols for Breast Cancer Chemoprevention
Nurulain Zaveri , Ph.D.
Stanford Research Institute, International
Preventing breast cancer is a major priority issue of the Breast Cancer Research Program. Cancer preventative agents from natural sources are of special interest. The proposed research aims to develop a new, safe breast cancer preventative drug based on a natural product found in green tea extracts. The natural product, EGCG (epigallocatechin - 3 - gallate), has shown cancer preventative activity in laboratory models of breast cancer. Systematic changes will be made in the structure of EGCG to find a compound with the best cancer preventative activity and fewest side effects.
At present, very few drugs are being developed as cancer chemopreventatives. Several naturally occurring substances have cancer chemopreventative properties, but very little research has been done to try to develop these compounds to get the best preventative effect combined with the lowest toxicity. This is the case with the green tea compounds. Green tea extract was shown to have cancer preventative effects in several experimental models of breast, lung, stomach and prostate cancer. EGCG, but not the other compounds of green tea extract, caused significant shrinkage of breast tumors in experimental models. This information suggests a link between a specific chemical structure and antitumor activity and gives a good starting point for research to develop an even more effective drug to prevent breast cancer. Because humans have used green tea as a common beverage for centuries, it is also likely that the new compound based on EGCG will be very safe - an important advantage. However, there are two reasons why drinking several cups of green tea a day as a breast cancer prevention strategy is impractical: many people do not like tea, and green tea does contain several components besides EGCG, some of which may be detrimental. Therefore, this research will use the structure of EGCG, the main chemopreventative ingredient of green tea, as a model to develop more powerful chemopreventatives.
This research will combine computer-aided drug design and laboratory synthesis of compounds to determine which structural features of EGCG are important for chemopreventative activity. New compounds will be designed and synthesized to allow systematic exploration of which changes give the strongest cancer preventative effect and the fewest unwanted effects. The advantages of the approach are that the drug development effort is based on a compound known to have cancer preventative effects, and computer modeling is an economical way to design similar compounds and predict their success without going to the expense of making all of them. All compounds synthesized will be tested in cell culture experiments to provide feedback for designing improved versions. This is an efficient way to find the few best compounds which are worth more extensive testing.
Postdoctoral Fellowship Award
Studies of Tamoxifen/Toremifene DNA Interactions in Monkeys
Utha Hellmann-Blumberg, Ph.D.
University of California, Davis
The antiestrogen tamoxifen has been the drug of choice since the early 1980's for the treatment of women with estrogen-receptor (ER) positive breast cancer and is sometimes hailed as a "wonder drug'. While it does prolong disease-free survival for several years after initial surgery, uncertainty exists about the optimum length of tamoxifen treatment, since it can actually cause cancer of the endometrium (lining of the uterus). Tamoxifen has also been shown to cause liver cancer in laboratory animals (rats). Experiments on rats demonstrate that tamoxifen binds to DNA and forms so-called adducts. DNA adducts are modifications of the DNA that lead to mutations and, if sufficient mutations accumulate, to cancer. An alternative drug, toremifene, also prevents the recurrence of breast cancer but does not form DNA adducts in rats. Conclusive data in humans, however, are not available at this point because of the difficulty of obtaining data on tamoxifen and toremifene DNA adducts relevant to human exposure. Because rats differ in many aspects from humans, a study will be initiated to test the effects of tamoxifen and toremifene treatment in monkeys. This data will be much more relevant to effects of these drugs on humans. We propose to determine whether and how much DNA adducts are formed in liver, endometrium and spleen of the monkeys at different time points during treatment with either drug. High levels of DNA adducts will show that the treatment is likely to cause new tumors. The long-term goal of this study is to obtain data that lead to new treatments for breast cancer.
