Declining incidence of contralateral breast cancer in the United States from 1975 to 2006.

PURPOSE: Contralateral breast cancer (CBC) is the most frequent new malignancy among women diagnosed with a first breast cancer. Although temporal trends for first breast cancers have been well studied, trends for CBC are not so well established.

PATIENTS AND METHODS: We examined temporal trends in CBC incidence using US Surveillance, Epidemiology, and End Results database (1975 to 2006). Data were stratified by estrogen receptor (ER) status of the first breast cancer for the available time period (1990+). We estimated the annual percent change (EAPC) in CBC rates using Poisson regression models adjusted for the age at and time since first breast cancer diagnosis.

RESULTS: Before 1985, CBC incidence rates were stable (EAPC, 0.27% per year; 95% CI, -0.4 to 0.9), after which they declined with an EAPC of -3.07% per year (95% CI, -3.5 to -2.7). From 1990 forward, the declines were restricted to CBC after an ER-positive cancer (EAPC, -3.18%; 95% CI, -4.2 to -2.2) with no clear decreases after an ER-negative cancer. Estimated current age-specific CBC rates (per 100/year) after an ER-positive first cancer were: 0.45 for first cancers diagnosed before age 30 years and 0.25 to 0.37 for age 30 years or older. Rates after an ER-negative cancer were higher: 1.26 before age 30 years, 0.85 for age 30 to 35 years, and 0.45 to 0.65 for age 40 or older.

CONCLUSION: Results show a favorable decrease of 3% per year for CBC incidence in the United States since 1985. This overall trend was driven by declining CBC rates after an ER-positive cancer, possibly because of the widespread usage of adjuvant hormone therapies, after the results of the Nolvadex Adjuvant Trial Organisation were published in 1983, and/or other adjuvant treatments.