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IMS reaction to report on breast cancer incidence in 2003 in US

April 19, 2007

A special report in the April 19 issue of the New England Journal of Medicine [1] brings initial analysis of data from the National Cancer Institute's Surveillance, Epidemiology and End Result (SEER) registries, showing that the incidence of breast cancer in women in the US fell by 6.7% in 2003, and stayed at the same level in 2004. The decrease was evident only in women who were 50 years of age or older, and solely involved cancers that were estrogen receptor-positive. The investigators suggested that a plausible explanation for the unexpected data is the concomitant sharp decrease in the use of postmenopausal hormones, which followed the first report from the Women's Health Initiative (WHI) study in mid-2002.

While being pleased with these new data on the incidence of breast cancer, the International Menopause Society (IMS) advises caution in linking these two parallel trends observed in the US. Any attempt to put both observations into one framework is premature and there is little scientific basis for such an assumption. In fact, the authors themselves mention in the manuscript that other factors might have contributed to these changes in breast cancer incidence. Nevertheless, the reader of the article still receives a clear message on the presumed association with hormone therapy (HT).

The IMS wishes to stress the following relevant facts:

- Despite a similar decrease in the use of HT in other countries as a result of the WHI results, such a decline in the incidence of breast cancer incidence in 2003 was not recorded by some other national cancer registries world-wide such as in the UK.

- According to Figure 1 in the article, a transient decrease in breast cancer incidence was observed also around 1987-9. There is no reason to associate that incidence with hormone use, which shows that other factors may play a role, or that unexplained epidemiological aberrations may occur.

- Possible confounders were not evaluated in this initial analysis of SEER data. Perhaps the most important ones are the rates of mammography and clinical breast exams. An abstract was presented in February 2007 by Dr Chagpar [2] at a congress of the Association for Academic Surgery and the Society of University Surgeons, showing that, according to data from the Centers for Disease Control and Prevention's National Health Interview Survey, both mammography and clinical breast cancer exam rates were significantly reduced in 2005 as compared to the 2000 figures. Thus, it remains unclear whether some or all the decline in breast cancer incidence observed in 2003 actually reflects an artifact caused by less screening.

- Current knowledge of the biology and development of breast cancer suggests that a 10% decrease in breast cancer incidence occurring within a year after cessation of estrogen therapy is unlikely.

- The WHI study has already provided very good epidemiological data on the association between HT and breast cancer risk. In the conjugated equine estrogen plus medroxyprogesterone acetate arm (5.2 years' follow-up), no risk was recorded for women who did not use HT prior to the study or were aged less than 60 years at randomization. The results in the conjugated estrogen-alone arm (6.8 years' follow-up) were more favorable, with fewer cases of invasive breast cancer in women entering the study before age 60. The availability of the results of the WHI study and other major observational studies (such as the Nurses' Health Study) makes the suggested link between a decrease in breast cancer incidence and the decrease in hormone use less important for the consumer, since risks of long-term HT can be reported accurately, based on the above randomized or cohort studies

The IMS maintains its recommendation that HT should be prescribed whenever indicated. The use of hormones in early menopause and up to age 60 years has a very minor potential for harm, but carries substantial benefits. Women should decide annually whether they wish to continue treatment after consultation with their caregiver [3].

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References

1. Ravdin PM, Cronin KA, Howlander N, et al. The decrease in breast cancer incidence in 2003 in the United States. N Engl J Med 2007;356:16
2. Chagpar AB, Scoggins CR, Martin II RC, McMasters KM. Trends in mammography and clinical breast examination: Results of a national population-based survey. Presented at the 2nd Annual Academic Surgical Congress, February 9, 2007
3. IMS Updated Recommendations on postmenopausal hormone therapy. Climacteric 2007;10:181-94

International Menopause Society