Introduction: A recent abstract presented in a breast cancer symposium attributed the sharp decrease in female breast cancer incidence rates from 2002 to 2003 in the Surveillance, Epidemiology, and End Results (SEER) cancer registries of the United States to the reduced use of hormone replacement therapy since July 2002. However, this hypothesis does not explain the decrease that began in 1999 in the age-standardized incidence rate of invasive breast cancer in the nine oldest SEER cancer registry areas, although the trend through 2003 was not statistically significant. In this paper, we examine temporal trends in invasive and in situ female breast cancer by age, stage, tumor size, and estrogen receptor/progestin receptor (ER/PR) status in the nine oldest SEER cancer registry areas and consider the implication of these trends in relation to risk factors and screening.
Methods: We performed a joinpoint regression analysis to fit a series of joined straight lines to the trends in age-adjusted rates and described the resultant trends (slope) by annual percentage change (two-sided, P < 0.05).
Results: A plot of the age-specific rates of invasive breast cancer shows a decrease in all 5-year age groups from 45 years and above between 1999 and 2003 and sharp decreases largely confined to ER+ tumors in age groups from 50 to 69 years between 2002 and 2003. In joinpoint analyses by tumor size and stage, incidence rates decreased for small tumors (less than or equal to 2 cm) by 4.1% (95% confidence interval [CI], 0.2% to 7.8%) per year from 2000 through 2003 and for localized disease by 3.1% (95% CI, 1.2% to 5.0%) per year from 1999 through 2003. No decrease in incidence was observed for larger tumors or advanced-stage disease during the corresponding periods. Rates for in situ disease were stable from 2000 through 2003 after increasing rapidly since 1981.
Conclusion: Two distinct patterns are observed in breast cancer trends. The downturn in incidence rates in all age groups above 45 years suggests a period effect that is consistent with saturation in screening mammography. The sharp decrease in incidence from 2002 to 2003 that occurred in women 50 to 69 years old who predominantly, but not exclusively, had ER+ tumors may reflect the early benefit of the reduced use of hormone replacement therapy.