Objective.-To describe trends in incidence and treatment for ductal carcinoma in situ (DCIS) of the breast in the United States between 1973 and 1992 and to estimate total numbers of in situ cases diagnosed and numbers treated by mastectomy since 1983, when screening mammography for breast cancer began to become widespread. Design.-Analysis of population-based breast cancer incidence data collected by the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program since 1973 and treatment data collected by the SEER program since 1983. Study Population.-All women in the geographic areas of the United States included in the SEER program. Main Outcome Measures.-Annual age-adjusted and age-specific incidence rates for DCIS; time trends in distribution of cases by type of treatment; percentage of cases treated by mastectomy by geographic area; and estimated numbers for the entire United States of DCIS cases, mastectomies for DCIS, and cases attributable to mammography. Results.-There was a marked increase in DCIS incidence beginning in the early 1980s. Average annual increases in rates between 1973 and 1983 and between 1983 and 1992 changed from 0.3% to 12.0% among women aged 30 to 39 years, from 0.4% to 17.4% among women aged 40 to 49 years, and from 5.2% to 18.1% among women aged 50 years or older. The total estimated number of DCIS cases in the United States in 1992 (23 368) was 200% higher than expected based on 1983 rates and trends between 1973 and 1983, Between 1983 and 1992, there was a marked decline in the proportion of DCIS cases treated by mastectomy (from 71% to 43.8%) and an increase in those treated by lumpectomy (from 25.6% to 53.3%). In 1992, 23.3% of cases were treated by lumpectomy and radiation, 30.2% by lumpectomy alone, and 2.6% with no surgery, Treatment patterns varied substantially by geographic area, with 57.7% of cases in New Mexico treated by mastectomy in 1992 compared with 28.8% in Connecticut, Despite the decline in the proportion of cases treated by mastectomy, the increased DCIS incidence rates resulted in an increase in the absolute number of cases treated by mastectomy until 1990 (n=10 657); in 1992, there were an estimated 10 242 DCIS cases treated by mastectomy. Conclusions-Incidence rates of DCIS of the breast have increased dramatically since 1983. This increase correlates with the widespread adoption of modern mammographic screening. While early detection of invasive breast cancer is beneficial, the value of DCIS detection is currently unknown. There is cause for concern about the large number of DCIS cases that are being diagnosed as a consequence of screening mammography, most of which are treated; by some form of surgery. In addition, the proportion of cases treated by mastectomy may be inappropriately high, particularly in some areas of the United States.
