Changes in Breast Cancer Incidence Rates

To the Editors: We read with interest the article by Li and Daling in which the authors reported that invasive ductal carcinoma and invasive lobular carcinoma incidence rates fell steadily from 1998 to 2004. The authors attributed these declines primarily to saturation of screening and secondarily to the widespread cessation of hormone use, which started in 2002 (1).

However, the authors made no reference to other established risk factors that could have changed during the study period, particularly the declining consumption of alcohol in the United States. Alcohol is an established, dose-dependent, risk factor for the development of estrogen receptor–positive breast cancer (2) and could be a contributing factor to the authors' observations. Alcohol consumption has been declining for decades in the United States. The National Institute on Alcohol Abuse and Alcoholism reported that the per capita consumption of alcohol by Americans had steadily declined by 10% from 1990 to 2000 and this trend seems to continue (3). The Harvard School of Public Health College Alcohol Study's survey documented an increase in the proportion of female college student abstainers and a decrease in the average number of drinks consumed by those who do drink in 2002 (4).

By contrast, we have not observed such a decline in invasive breast cancer incidence rates in the United Kingdom despite the saturation of the national screening program and widespread publicity associated with the Women's Health Initiative findings (5). In the southeast of England where incidence statistics are available,¹

the age-standardized incidence rate for all age groups combined has increased gradually since 1960, reaching a peak in 1997. The age-standardized rates increased in each of the prescreening, screening, and postscreening age groups, with the rates in the screening group (ages 50-64 years) rising most sharply between 1988 and 1992, coinciding with the introduction of the national screening program, which reached saturation by 1997. Women's changing reproductive history and increased exposure to risk factors, such as hormone replacement therapy and alcohol consumption, are widely regarded to be partly responsible for the steadily increasing incidence rates observed across all age groups in the period 1960 to 1997. Between 1998 and 2004, the incidence rates in each age group have remained fairly constant with no significant decline due to either saturation of screening or hormone replacement therapy cessation. This suggests that other risk factors such as increasing alcohol consumption in the United Kingdom could be driving up breast cancer incidence rates, thus counteracting the effects of screening saturation and declining use of hormone replacement therapy. The average weekly consumption among women has increased by 40% during 1992 to 2002 according to the Office of National Statistics in the Great Britain (6).