Disuse of hormone therapy might have fueled a significant drop in breast cancer detection rates in recent years, but a plateau in screening mammography among women older than 45 also contributed to the decline, according to new data from American Cancer Society.
To assess breast cancer trends before the Women’s Health Initiative suggested a link between hormone therapy and breast cancer, the American Cancer Society reviewed data from the nine oldest Surveillance, Epidemiology, and End Results cancer registries. Based on these registries, 394,891 invasive and 59,837 in situ breast cancer cases were diagnosed in US women aged 40 and older from 1975 through 2003. Age-specific incidence of invasive breast cancer declined in all five-year age brackets for women aged 45 and older between 1999 and 2003. The decrease in breast cancer incidence among most women younger than 60 or older than 69 began in 1998 or 1999; the decrease in women aged 60-64 and 65-69 occurred from 2002 to 2003 (the most recent year for which data are available). The largest percentage decreases occurred from 2002 to 2003 in women aged 55-59 (11.3%), 60-64 (10.6%), and 65-69 (14.35).
A joint analysis of tumor size and stage showed that overall, the incidence of small tumors (2 cm or less) decreased by 4.1% per year from 2000 through 2003 and the incidence of localized disease fell by 3.1% per year from 1999 through 2003. No decrease in the incidence of larger tumors or advanced-stage disease was found. Also, in situ disease rates were stable from 2000 through 2003 after increasing since 1981.
Trend data based on receptor status showed an annual increase in the incidence of both estrogen receptor-positive tumors and progestin receptor-positive tumors from 1990 to 2000, then a 9.1 drop from 2002 to 2003 for both types. Estrogen receptor-negative and progestin receptor-negative tumors also showed their largest overall decreases in incidence, 4.8% and 6.9% respectively, between 2002 and 2003. Two patterns of breast cancer trends emerged.
First, the drop in incidence that began in 1998 coincides with a plateau in screening mammography, and the types of cancers detected by mammography were the types that had a decrease in incidence (small tumors and localized disease). National Health Interview Survey data show that the percentage of women aged 40 and older who reported having mammogram in the past 2 years as 70.3% in 1999, 70.4% in 2000, and 69.5% in 2003. “Typically, incidence rates decrease when the penetrance of a screening test reaches a plateau due to reduced pool of undiagnosed prevalent cases. Second, the sharp declines in breast cancer from 2002 to 2003 that were reported at a breast cancer symposium sponsored by the Cancer Therapy and Research Center last year might have been due in part to a reduced use of hormone therapy in response to data from the Women’s Health Initiative that linked hormone therapy to an increased risk of breast cancer. The sharp drop was observed mainly in estrogen receptor-positive tumors in a subset of women aged 50-69.
Clearly there are many of us who feel that (the) drop in breast cancer detection rate has many factors. The falloff in detection is much greater than one would have expected from hormones alone.