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The "Epidemic" of Breast Cancer in the U.S.--Determining the Factors

The "Epidemic" of Breast Cancer in the U.S.--Determining the Factors

It is perhaps not surprising that the increased incidence of a disease that has a major impact on mortality in young women (even though the absolute risk of death from breast cancer in this age group is low) should create so much interest. Yet, despite decades of research, it is by no means clear that everyone would agree with King and Schottenfeld that the appropriate approach to breast cancer prevention is one that "focuses on the physiologic effects of the sex steroid hormones and their potential interactions with family history." However, this tantalizing statement appearing at the end of the abstract of their article fortunately is elaborated upon at the end of the article itself. This elaboration refers specifically to physical activity, energy consumption, obesity, pregnancy history and exogenous estrogens and their potential interactions with family history, with which many will agree.

King and Schottenfeld rightly comment on the discrepancy between rising incidence and stable mortality and attribute much of the increase in incidence, particularly that occurring recently, to screening. I agree with them. I also think that their statement does not go far enough, in that much of the earlier increase (at least during the 1950s) was also due to improvements in early diagnosis caused by the increasing availability of skilled radiologists, clinicians, and pathologists, whose talents were brought to bear on the concerns of women, amplified by the publicity surrounding breast cancer generated by the cancer societies. Thus, most of the increases have resulted from a combination of earlier lead time, ie, the bringing forward in time of the diagnosis of a case that would have occurred later; and overdiagnosis, the identification of a case that would never have surfaced without the screening test or diagnostic proceedure.

It is clear from international comparisons that increasing affluence and westernization have a major impact on breast cancer incidence. This has been seen in a number of countries that have made the epidemiologic transition from the dominance of cancer of the cervix to the dominance of cancer of the breast. These countries include Singapore, Hong Kong, and other countries of Southeast Asia, and even Bombay, India. The cancer registries of these countries have shown that as the incidence of cervical cancer has fallen, the incidence of breast cancer has risen.

This crossover marks a transition of women through the effects of westernization that they would not necessarily have desired. There seems little doubt that this transition is caused by a combination of different changes in lifestyle, with the effect of diet probably dominant, accompanied by diminishing exercise, increasing obesity, increasing alcohol consumption, and changes in age at first birth. The effect of nutrition in these countries is perhaps most obvious in the declining age at menarche.

Given these changes occurring elsewhere and their likely continued impact in North America, is there any residual role for organochlorines or other environmental exposures? King and Schottenfeld do not appear to have reached a conclusion about this issue. Adami et al [1] have recently published a review in which they conclude "that available data do not indicate that organochlorines will affect the risk of these two cancers [breast cancer and endometrial cancer] in any but the most unusual situation." A few months ago I would have agreed with that conclusion. Now findings from our pilot study indicate excess dichlorodiphenyltrichloroethane (DDT), hexachlorobenzene and polychlorinated biphenyls (PCB) residues in the breast fat of newly diagnosed women with breast cancer, compared to the breast fat of comparable women with benign breast disease used as controls [2]. It is not clear whether the organochlorines here are really acting as a marker of exposure, as we had anticipated, or as a marker of different metabolism of these substances in breasts where carcinogenesis is already in progress. This will require more detailed investigations at the molecular level.

Practical Advice for Decreasing Breast Cancer Risk

In the meantime, can we take the information on risk factors reviewed by King and Schottenfeld and turn it into advice on what women can do to reduce their risk of breast cancer, and particularly how physicians can advise them in this regard? In my view, mothers need to be reminded that the lifestyle habits that their daughters adopt will affect their future breast cancer risk. This relates particularly to diet and exercise. The negative findings from the cohort studies commented upon by King and Schottenfeld apply only to diet in adult life. The international comparisons and the slow changes in incidence on migration from a low- to a high-risk area reinforce the role of diet in early life.

Young women should also be aware of the effects of delayed age at first birth in increasing the risk of breast cancer, although it seems unlikely that such knowledge will reverse the present trends. Furthermore, they should be aware that maintaining appropriate body weight throughout their life, combined with suitable exercise and dietary regimens, will help keep them in a lower-risk group for breast cancer.

In addition, young women need to make informed decisions about the use of oral contraceptives and hormone replacement therapy, although in both instances it seems likely that other effects of these hormones besides those related to breast cancer will have a stronger influence on the decision. They should also be aware of the effect of screening in bringing forward the date of diagnosis and therefore contributing to the "epidemic" of breast cancer, which is really not an epidemic at all. Whether or not they should use mammography is another issue that I raised in a commentary published in a recent issue of this journal.

However, perhaps most important of all is to stop talking about an epidemic of breast cancer. Women should recognize that they are not powerless and may be able to help reduce their risk by appropriate lifestyle choices.

References

1. Adami HO, Lipworth L, Titus-Erstoff L, et al: Organolchlorine compounds and estrogen-related cancers in women. Cancer Causes Control 6:551-566, 1995.

2. Aronson KJ, Miller AB, Hanna W, et al: Pesticides and polychlorinated biphenyls: associations with breast cancer. Submitted to JNCI, 1996.

 
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