A new study, published in the Online Open Access journal Breast Cancer Research, reveals two distinct patterns in the recent breast cancer rates in U.S. women: a downturn in the incidence rates in almost all age groups above 45 years beginning in 1998/1999, consistent with a levelling off of mammography utilization, and a sharp fall in the rates between 2002 and 2003 in the age groups 50-69 years, likely reflecting the early benefit of the reduced use of HRT.
Previous studies have suggested a link between HRT use and breast cancer. Ahmedin Jemal and colleagues at the American Cancer Society conducted statistical analysis to examine patterns in invasive and in situ breast cancer incidence in relation to age, tumour size at diagnosis and disease stage. Regular mammography screening starts at 40 and HRT is most common in women aged 50 or older, so the study focussed on women age 40 and above.
The research team examined trends in breast cancer incidence in the National Cancer Institute's Surveillance Epidemiology and End Results database from 1975 to 2003. The database includes women from 5 US States (Connecticut, Hawaii, Iowa, New Mexico, and Utah) and 5 metropolitan cities (Atlanta, Detroit, San-Francisco, and Seattle). Almost 400,000 invasive and 60,000 in situ cases of breast cancer were diagnosed in that time. Breast cancer incidence rates increased by almost 40% between 1980 and 1998, and then showed a downward trend with a dramatic decrease from 2002 to 2003. The greatest decline was in women who had small tumours, early stage disease, estrogen/progestin positive tumours, and who were aged 55 or older.
Jemal et al concluded that the speed of decrease in breast cancer incidence, following the dramatic reduction in HRT use after the Women's Health initiative publication in 2002, likely reflects the early consequences of reductions in HRT use, while the downturn in incidence rates across multiple age groups beginning 1998/1999 reflects the saturation of mammography.
Recent Trends in Breast Cancer Incidence Rates by Age and Tumor Characteristics among U.S. Women
Ahmedin Jemal, Elizabeth Ward and Michael J Thun
Breast Cancer Research (In press)