Breast Cancer Decline Linked to Decrease in Hormone Use, not Less Screening

Decreased use of postmenopausal hormone therapy since 2002 – rather than a decrease in screening – has contributed to a decline in the recorded incidence of breast cancer in the United States, according to Patty Carney, Ph.D, Oregon Health and Science University Cancer Institute.

The study involved more than 600,000 mammograms and has been published online in the Aug. 14, 2007 Journal of the National Cancer Institute and appears in the Sept. 5, 2007 print issue. This is the first study to investigate breast cancer incidence and hormone therapy use in a population of women having routine mammograms. “Prior research on the declines in HRT (hormone replacement therapy) and breast cancer were ecological in nature in that there was an inadequate link between factors that may have affected the findings. We used a very powerful dataset to examine whether the decrease in breast cancer occurred in routinely screened women who would remove the issue of surveillance bias from the question about why breast cancer incidence is falling,” said Carney, senior author of the study. She is also a professor of family medicine and public health and preventive medicine, OHSU School of Medicine, director, Community Research and Engagement Program, Oregon Clinical and Translational Research Institute, associate director for Population Studies.The researchers collected data on 603,411 mammograms between 1997 and 2003 on women aged 50 to 69 from four screening registries in the United States. Between 2000 and 2003, use of hormone therapy among the study group declined by 7 percent a year between 2000 and 2002, then by 34 percent a year between 2002 and 2003. During the same period, breast cancer rates declined annually by 5 percent. Oestrogen-receptor positive breast cancer fell by 13 percent each year from 2001 to 2003. There has been a decline in postmenopausal hormone therapy use since 2002 when the Women’s Health Initiative study found that hormone therapy was associated with an increased risk of breast cancer. Recent data has linked breast cancer decline to hormone use but also perhaps to a decrease in mammography screening. The researchers speculate that oestrogen and progestin work synergistically to promote breast tumour formation and growth. In the absence of those hormones, tumours may grow very slowly, stop growing, or regress completely, which would account for the drop in oestrogen receptor-positive breast cancer rates. This study suggests that a decline in postmenopausal hormone use has contributed to fewer breast cancers in the United States. The decline in mammography is unlikely the cause for the decline in breast cancer incidence, the study authors concluded.”What this means is that women who require oestrogen-progestin therapy to control postmenopausal symptoms should be encouraged to use the therapy for the shortest time possible to minimize breast cancer risk,” Carney said. The lead author is Karla Kerlikowske, M.D., San Francisco Veterans Affairs Medical Center; and professor of medicine, epidemiology and biostatistics, University of California, San Francisco.Other researchers include: Diana L. Miglioretti, Ph.D., Group Health Center for Health Studies(GHCHS) Seattle, and the University of Washington (UW); Diana S.M. Buist, Ph.D., GHCHS; and Rod Walker,GHCHS and UW. All authors participate in the Breast Cancer Surveillance Consortium (http://breastscreening.cancer.gov/).The research was supported by funds from the National Cancer Institute. (Source: Christine Decker : Oregon Health and Science University : November 2007)