Decline in Breast Cancer and Reduced Use of Hormone Therapy

Abstract & Commentary

By Leon Speroff, MD, Editor, Professor of Obstetrics and Gynecology, Oregon Health and Science University, Portland, is Editor for OB/GYN Clinical Alert.

Synopsis: Breast cancer statistics indicate a rapid decrease in prevalence immediately after the publicity surrounding the reports from the Women's Health Initiative.

Source: Ravdin PM, et al. A sharp decrease in breast cancer incidence in the United States in 2003. San Antonio Breast Cancer Symposium, December 14, 2006.

Ravdin and colleagues from the University of Texas M.D. Anderson Cancer Center reported a 7% decrease (14,000 fewer cases) in the incidence of breast cancer in 9 regions of the U.S. in 2003.1 This decrease occurred in women over age 50 and consisted of two to three times as many estrogen receptor positive tumors. The steepest decline was observed in women ages 50-69. Clarke and colleagues from California reported the breast cancer incidence for the years 2003 and 2004 in the Northern California Kaiser program and for the 13-county Kaiser catchment area.2 Coincident with the post-Women's Health Initiative decline in postmenopausal hormone use, the breast cancer incidence declined 10% in Kaiser members and 11% in the area's population.

Commentary

These reports highlight the currently most important unanswered question: Does postmenopausal hormone therapy cause an increase in breast cancer or do the epidemiologic data reflect an impact of hormone therapy on pre-existing tumors? The most striking feature of these recent reports is the short latent period between discontinuation of hormone therapy and a reduction in prevalence. This is consistent with the uniform findings in case-control and cohort studies of an increase in breast cancer risk only in current users, with a rapid reduction after cessation of treatment. The current reports are consistent with breast cancer statistics derived from the area around Geneva, Switzerland, indicating the other side of the coin. Beginning in 1997, the peak of breast cancer incidence in the Geneva area increased in a younger group of women (ages 60-64), and the increase occurred only in Stage I and Stage II disease with estrogen receptor positive tumors in hormone users.3

These effects of hormone therapy are in keeping with the multiple reports of better outcomes in hormone users diagnosed with breast cancer because of better-differentiated tumors,4, 5 an effect that can be interpreted as a beneficial consequence. Another finding that is consistent with an effect on pre-existing tumors is the fact that not a single study thus far has reported a risk increase for non-invasive disease. If hormone therapy were initiating (causing) new tumor formation, one would expect to see an increase in in-situ disease.

Even the M.D. Anderson Cancer Center authors pointed out that their data most likely primarily reflect existing cancers just below the detection limit in 2002 that slow or stop their growing. Thus, a serious question is raised: What will the statistical data show in the coming years? Will some of the pre-existing tumors be overcome by body defenses and disappear? Will tumors that emerge later be of later stage and grade disease with poorer outcomes? At this point in time, we must recognize that hormone therapy could be having a favorable effect on breast cancers.

References

  1. Ravdin PM, et al. A sharp decrease in breast cancer incidence in the United States in 2003. San Antonio Breast Cancer Symposium, December 14, 2006.
  2. Clarke CA, et al. Recent declines in hormone therapy utilization and breast cancer incidence: clinical and population-based evidence. J Clin Oncol. 2006;24:e49-e50.
  3. Bouchardy C, et al. Remarkable change in age-specific breast cancer incidence in the Swiss canton of Geneva and its possible relation with the use of hormone replacement therapy. BMC Cancer. 2006;6:78-85.
  4. Gertig DM, et al. Duration of hormone replacement therapy, breast tumour size and grade in a screening programme. Breast Cancer Res Treat. 2003;80:267-273.
  5. Pappo I, et al. The characteristics of malignant breast tumors in hormone replacement therapy users versus nonusers. Ann Surg Oncol. 2004;11:52-58.