Ref. #15099

Medical/Scientific Viewpoints on Breast Cancer

Environmental Factors and Women's Health

Selected Excerpts From Scientists and Medical Researchers Regarding Breast Cancer and Related Issues

I. Breast Cancer in the United States Today

"Much of the recent increase in cancer incidence can be explained by known risk factors. Improved detection appears to account for most of the increases in breast cancer among women ... Increasing exposure to general environmental hazards seems unlikely to have had a major impact on the overall trends in cancer rates." Susan Devasa, Ph.D., The National Cancer Institute [1]

"... there is reason to believe that much, if not most, of the apparent epidemic of breast cancer is due to increased detection of cancers that might never have become clinically important." Dr. Virginia Ernster, University of California at San Francisco [2]

"[A] substantial proportion of breast cancer cases in the United States are explained by well-established risk factors... We estimate that about 41% of breast cancer cases in the United States were attributable to later age at first birth, nulliparity (never giving birth), family history of breast cancer, and higher socioeconomic status." M. Patricia Madigan, National Cancer Institute [3]

"One of the major contributors to the high rates of breast cancer among women in the Northeast was the tendency of Northeastern women to have had, on average, first births at later ages. It has long been known that risk of breast cancer increases nearly linearly with advancing age at first birth. Indeed, from the summary data presented by the authors, it can be calculated that the risk of breast cancer increases about 7-8% with every year of delay in the birth of the first child, so that even small regional differences in reproductive patterns can have measurable impacts on breast cancer rates." William J. Blot, Ph.D., International Epidemiology Institute [4]

"The findings of the National Cancer Institute should help allay fears that unknown environmental hazards are responsible for the clustering of elevated breast cancer mortality in the Northeast... The causes of this common cancer are not fully understood, but the research reported in this issue of the Journal indicates that most of the geographic variation in breast cancer mortality among American women appears due to variation in known reproductive and other risk factors." William J. Blot, Ph.D., International Epidemiology Institute [4]

"... the death rate for breast cancer in American women declined 4.7 percent between 1989 and 1992, the largest such short-term decline in the United States for this disease since 1950... Much research will be needed to understand the specific reasons for the declining rates, Dr. (Samuel) Broder (NCI's Director) told the (National Cancer Advisory) Board. 'We believe that several factors are involved, including adjuvant therapy for breast cancer, breast cancer awareness and screening with mammography and clinical exam, and changes in risk factors.'" National Cancer Institute [5]

II. Organochlorine Compounds and Related Issues

"The data (from the Kaiser Study) do not support the hypothesis that exposure to DDE and PCBs increases risk of breast cancer." Nancy Krieger, et al, Journal of the National Cancer Institute [6]

"The Journal (Journal of the National Cancer Institute) brings another reminder of the caution with which the results of a single epidemiological study, or even a handful of them, should be regarded ... The Kaiser study has a number of features that favor its conclusions." Brian MacMahon, Ph.D., Harvard School of Public Health [7]

"Contemporary human exposures to residues of dichlorodiphenyl trichlorethane (DDT) and other organochlorines are very limited, and therefore this source of exposure seems biologically insignificant compared to other exogenous sources such as oral contraceptives, estrogen replacement regimes and phytoestrogens in food." Leonard Ritter, Ph.D., Canadian Network of Toxicology Centres [8]

"The epidemiological findings regarding the association between organochlorines and breast cancer are inconclusive ... It is questionable whether the background levels of organochlorines in the general population will be high enough to elicit any of these effects." Ulf Ahlborg, Karolinska Institute, Stockholm [9]

"(An epidemiological review conducted by the International Agency for Research on Cancer (IARC) in 1985) concluded that DDT has had no significant impact on human cancer patterns and is unlikely to be a carcinogen at historical exposure levels ... While it is biologically plausible that DDT exposure could be a minor risk factor for breast cancer, the evidence is not compelling. Reviews by IARC, and the largest prospective study conducted to date (Kaiser) do not support an association." Leonard Ritter, Ph.D., Canadian Network of Toxicology Centres [10]

"In humans, neither ecologic data nor occupational studies provide clear support for an association between organochlorine exposure and the occurrence of these cancers (breast and endometrial) ... We conclude that available data do not indicate that organochlorines will affect the risk of these two cancers in any but the most unusual situation." Dr. Hans-Olov Adami, Uppsala University, Sweden [11]

"I suggest that more caution be taken in ascribing possible causation of breast cancer to DDT and other organochlorines. The media and the public have a tendency to misinterpret or indulge in hyperbole in evaluating such reports... My immediate fear is that funding may be misdirected, resulting in epidemiologic studies with less-than-satisfactory conclusions that would be often dependent on statistical nuances." Stephen S. Steinberg, M.D., Memorial Sloan-Kettering Cancer Center [12]

"Our studies [Mount Sinai] have received some attention because of their uniqueness and because of their potential impact on public health, but much remains to be done to confirm the findings linking organochlorines to breast cancer and to clarify the underlying mechanisms." Dr. Mary Wolff [13]

III. Estrogen, Sources of Estrogen and Breast Cancer Risks

"Estrogens in drugs and naturally-occurring in food are far more potent than the estrogenic activity from certain chemical compounds. "Following are estimated daily doses in terms of estrogen equivalents [chart taken from study]:

Morning after pill		333,500 times
Birth control pill		16,675 times
Post-menopausal therapy		3,350 times
Flavonoids (Naturally occurring estrogens in food)		103 times
Environmental organochlorine estrogens		0.0000025 times

"[This illustrates] the minimal potential of these industrial estrogens to cause an adverse endocrine-related response in humans... "Moreover, dietary levels of antiestrogen equivalents (industrial or natural) are significantly higher than the estrogen equivalents of organochlorine pesticides. The suggestion that industrial estrogenic chemicals contribute to an increased incidence of breast cancer in women and male reproductive problems is not plausible...

"These results suggest that the increasing incidence of human breast cancer is not related to organochlorine environmental contaminants... The hypothesized linkage between dietary/environmental estrogens and the increased incidence of breast cancer is unproven." Stephen H. Safe, Ph.D., Texas A&M University [14]

"It is becoming clear that a number of foreign chemicals can bind to hormone receptors as well, although generally they bind more weakly than do the genuine hormone molecules... What is less clear is whether the small concentrations of xeno-estrogens [synthetic chemicals] usually experienced by most humans are capable of having any significant biological effect. The quantities involved are small; they are typically dwarfed by our intake of naturally occurring estrogenic compounds that are found in a variety of vegetables in our diet." Lorenz Rhomberg, Ph.D [15]

"Exposure to phytoestrogens is in turn dwarfed by the doses that many humans receive in birth control pills or post-menopausal hormone replacement therapy. Modern birth control pills have not been associated with elevated cancer risks... Some scientists have questioned whether the low levels of manmade xenoestrogens in the environment can plausibly be thought to affect the risks of hormonally influenced cancers when the exposure levels are over a hundred-fold less than exposures to estrogens in birth control pills." Lorenz Rhomberg, Ph.D [15]

"The assertion that widespread exposure to low levels of environmental chemicals has contributed to the incidence of breast cancer and other hormone related diseases is only a hypothesis. The available data are not sufficient to either clearly confirm or refute it." Chemical Industry Institute of Technology [16]

"The data so far produced provide reassurance rather than anxiety... [E]ven in large doses DDT is only weakly oestrogenic in animals, and it has not been shown to have oestrogenic effects in women. Oestrogen replacement therapy, which has clear oestrogenic effects, may increase the risk of breast cancer by about 30% after 15 years of use, so any small oestrogenic effect of DDT in the environment would probably be impossible to detect by epidemiological studies... Putting all the evidence together, we conclude that it is unlikely that DDT in the environment increases the risk of breast cancer." Timothy Key and Gillian Reeves, Oxford University [17]

"It is by no means certain that the health consequences in humans are caused by mimicry of estrogen. Karl T. Kelsey of the Harvard School of Public Health points out that 'although PCBs and DDT metabolites have been shown to have estrogen-like activity, other compounds such as birth control pills that have orders of magnitude more activity have not been definitely associated with breast cancer. So it's hard to understand how these compounds [PCBs and DDT] could be active when those are not'." John Rennie, Scientific American [18]

Bibliography

1. "Recent Cancer Trends in the United States," by Susan Devesa, Ph.D. (National Cancer Institute) et al., Journal of the National Cancer Institute, Vol. 87, No. 3, February 1, 1995.

2. "Known Risk Factors for Breast Cancer," discussion led by Dr. Virginia Ernster, University of California at San Francisco, at The Toxicology Forum, February 21-23, 1994, Washington, DC.

3. "Proportion of Breast Cancer Cases in the United States Explained by Well-Established Risk Factors," by M. Patricia Madigan (National Cancer Institute) et al., Journal of the National Cancer Institute, Vol. 87, No. 22, November 15, 1995.

4. "Geographic Patterns of Breast Cancer Among American Women," William J. Blot, Ph.D. and Joseph K. McLaughlin, Ph.D., International Epidemiology Institute, Journal of the National Cancer Institute, Vol. 87, No. 24, December 20, 1995. Editorial accompanied the following NCI study: "Geographic Variation in Mortality from Breast Cancer Among White Women in the United States," by Susan R. Sturgeon, Dr. P.H. et al.

5. "Breast Cancer Deaths Decline Nearly 5 Percent," Cancer Facts, National Cancer Institute, National Institutes of Health, press statement, January 13, 1995.

6. "Breast Cancer and Serum Organochlorines: A Prospective Study Among White, Black, and Asian Women," by Nancy Krieger et al., Journal of the National Cancer Institute, Vol. 86, No. 8, April 20, 1994.

7. "Pesticide Residues and Breast Cancer?" by Brian MacMahon, Ph.D., Harvard School of Public Health, Journal of the National Cancer Institute, Vol. 86, No. 8, April 20, 1994.

8. "Organochlorine Residues and Risk of Breast Cancer," by Leonard Ritter, Ph.D., Canadian Network of Toxicology Centres, University of Guelph, Public Health and Epidemiology Reports of Ontario, Vol. 5, No. 8, August 1994.

9. "Organochlorine Compounds in Relation to Breast Cancer, Endometrial Cancer, and Endometriosis: An Assessment of the Biological and Epidemiological Evidence," by Ulf G. Ahlborg (Karolinska Institute, Stockholm, Sweden) et al., Critical Reviews in Toxicology, Vol. 25, No. 6, 1995.

10. "Organochlorine Residues and Risk of Breast Cancer," by Leonard Ritter, Ph.D., Canadian Network of Toxicology Centres, University of Guelph, Public Health and Epidemiology Reports of Ontario, Vol. 5, No. 8, August 26, 1994.

11. "Organochlorine Compounds and Estrogen-Related Cancers in Women," by Dr. Hans-Olov Adami (Uppsala University, Uppsala, Sweden) et al., Cancer Causes and Control, Vol. 6, 1995.

12. A letter from Stephen S. Steinberg, M.D., Memorial Sloan-Kettering Cancer Center, Journal of the National Cancer Institute, Vol. 86, No. 1, January 5, 1994.

13. Testimony by Dr. Mary Wolff before the Subcommittee on Health and the Environment, U.S. House of Representatives, October 21, 1993.

14. "Environmental and Dietary Estrogens and Human Health: Is There a Problem?" by Stephen H. Safe, Ph.D., Texas A&M University, Environmental Health Perspectives, Vol. 103, No. 4, April 1995.

15. "Are Chemicals in the Environment Disrupting Hormonal Control of Growth and Development?," Lorenz Rhomberg, Ph.D., Risk in Perspective, Harvard Center for Risk Analysis, Vol. 4, No. 3, April 1996.

16. "The Endocrine Mystery and CIIT's Role in Finding the Answers," CIIT Insights, Chemical Industry Institute of Technology, March 19, 1996.

17. "Organochlorines in the Environment and Breast Cancer," by Timothy Key and Gillian Reeves, University of Oxford, letter to the British Medical Journal, Vol. 308, June 11, 1994.

18. "Malignant Mimicry," John Rennie, Scientific American, September 1993.