Hormone Therapy and Mammography Use Influence Breast Cancer Rates
Behind the Cancer Headlines®
July 30, 2007
A rise in breast cancer incidence from the 1980s through 2001 paralleled trends in mammography screening and hormone therapy use, while a recent decline in incidence was consistent with a drop in hormone therapy use, according to a study of a large group of women enrolled in a single health plan. The study was published in the Journal of the National Cancer Institute.
Breast cancer incidence has been on the rise since the late 1930s, but a recent report showed the first statistically significant decline in breast cancer incidence in 2003. Over this period, rates of hormone therapy use and mammography screening have changed too, but their individual influence on breast cancer rates was unclear.
Andrew Glass, M.D., of Kaiser Permanente’s Center for Health Research in Portland, Ore., and colleagues compared breast cancer incidence rates with mammography use and menopausal hormone therapy prescriptions among patients in the health plan between 1980 and 2006.
Among women 45 years and older, breast cancer incidence rose 25% from the early 1980s to the early 1990s and continued to rise but at a lower rate—15%—through 2001. The rates dropped by 18% from 2003 to 2004, and then edged up slightly in 2005 and 2006. This pattern was seen predominantly in estrogen receptor-positive breast cancers. Meanwhile, mammography screening rose from 1980 until 1993, then remained stable through 2006. Hormone therapy use increased from 1988 to 2002, when it dropped by 75%.
“This rise [from the early 1980s to 2001] seemed to occur in two phases, the first during the 1980s, coinciding with the progressive adoption of screening mammography by 75%-79% of eligible women in the plan, and the second corresponding to increases in menopausal hormone use, particularly combined therapy, throughout the 1990s,” the authors write.
In an accompanying editorial, Donald Berry, Ph.D., and Peter Ravdin, M.D., of the University of Texas M. D. Anderson Cancer Center in Houston suggest that hormone therapy itself may not cause breast cancer. Instead it could promote tumor growth while its withdrawal may slow or stop it. They add that using individual-based—in addition to population-based—data would give researchers a better picture of relationship between hormone therapy use and breast cancer.
“These additional analyses will be hopefully forthcoming from registries and data resources like those of the [Kaiser Permanente Northwest] group and might allow new insights into how to use menopausal hormone therapy with the lowest risk of negative effects and to the greatest advantage,” the editorialists write.
Journal of the National Cancer Institute, July 28, 2007