Correspondence

The One-In-Nine Risk of Breast Cancer

N Engl J Med 1999; 340:1839-1840June 10, 1999

Article

To the Editor:

Phillips et al. (Jan. 14 issue)1 are to be commended for their lucid deconstruction of the “one in nine” statistic, a figure seized on by the lay and medical media and one that has aroused concern that we are facing an unprecedented increase in breast cancer since it was first reported. However, missing from their discussion is any acknowledgment that life-table analysis of risk, such as that presented in Table 1 and Figure 1 of their article, applies only to the population from which the data were collected.

To the extent that breast cancer and cardiovascular disease are not genetically mediated, there is reason to suspect that the cohort of North American women currently in their 40s may not conform to the incidence and mortality profiles of the cohort currently in their 70s. For example, even if the possible effect of improved therapies on future mortality rates is not considered, these cohorts can be equivalent only if there has been no shift toward healthier lifestyles, if patterns of childbearing (e.g., maternal age at birth of a first child) have not changed, and if the rates of exposure to mammary carcinogens have remained stable over the past 40 years. None of these underlying assumptions seem sustainable. Thus, as several of my well-informed patients have pointed out, it is misleading to tell a group of 970 perimenopausal women that, on average, 105 of them will die of cardiovascular disease between the ages of 60 and 70 and 18 of them will die of breast cancer at that age. In truth, nobody knows what the figures will be.

In my experience, the typical 45-year-old woman whom one counsels about the risks of breast cancer and atherosclerosis has no familial risk factors and is already leading an active, semivegetarian lifestyle designed to promote cardiovascular fitness. Since life-table data, though imperfect as a predictive tool, are the best we have to go on, it would be helpful to see the numbers for the subgroup consisting of physically active women with good cholesterol values and no history of smoking. Perhaps the authors of this useful and widely quoted discussion can provide us with such statistics.

Barbara B. Harrell, M.D.
8009 40th Ave., NE, Seattle, WA 98115-4928

1 References

1. 1

   Phillips K-A, Glendon G, Knight JA. Putting the risk of breast cancer in perspective. N Engl J Med 1999;340:141-144
   Full Text | Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: Dr. Harrell is correct in pointing out that the statistics we presented are derived from a snapshot of the general population, which varies with respect to exposure to risk factors and protective factors (both known and unknown) for various diseases. It was not our intent to imply that a life table based on data from the general population can be used to determine an individual woman's exact risk of breast cancer or of death from breast cancer. In fact, given our imperfect understanding of the cause of breast cancer, it is currently not possible to provide a completely accurate estimate of an individual woman's risk, although attempts have been made.1,2

Analysis according to birth cohort is a useful way to assess variations in risk that may occur because of changes in exposure to risk factors over time. In keeping with Harrell's comments, it is interesting that Tarone et al.,3 contrary to their expectations based on trends in reproductive factors, found that the risk of death from breast cancer decreased among women born after 1950.

When educating a population of women, it is appropriate to use estimates of the risk of breast cancer that are derived from that population. Of course, we agree that when counseling an individual woman, one should supplement these general estimates of risk with a discussion of the specific risk factors relevant to that person.

We included the life table in order to convey general concepts about the age distribution and relative magnitude of the risk of breast cancer as compared with the risk of cardiovascular disease. Any estimate of the risk associated with a complex, multifactorial disease has inherent limitations. This fact only serves to highlight our concern about the extensive use of the one-in-nine statistic without any elaboration. This is the only information on the risk of breast cancer that many women receive, and we believe that it is inadequate and potentially misleading.

Kelly-Anne Phillips, M.B., B.S.
Peter MacCallum Cancer Institute, Melbourne 3000, Australia

Gordon Glendon, M.Sc.
Ontario Cancer Genetics Network

Julia Knight, Ph.D.
Cancer Care Ontario, Toronto, ON M5G 2L7, Canada

3 References

1. 1

   Gail MH, Brinton LA, Byar DP, et al. Projecting individualized probabilities of developing breast cancer for white females who are being examined annually. J Natl Cancer Inst 1989;81:1879-1886
   CrossRef | Web of Science | Medline

2. 2

   Claus EB, Risch N, Thompson WD. Autosomal dominant inheritance of early-onset breast cancer: implications for risk prediction. Cancer 1994;73:643-651
   CrossRef | Web of Science | Medline

3. 3

   Tarone RE, Chu KC, Gaudette LA. Birth cohort and calendar period trends in breast cancer mortality in the United States and Canada. J Natl Cancer Inst 1997;89:251-256
   CrossRef | Web of Science | Medline