Incidence of Dutal Carcinoma In Situ
Because of the adoption of screening mammography, reseachers have found a dramatic increase in the incidence of ductal carcinoma in situ (DCIS) during the past 20 years. 1 According to Surveillance Epidemiology and End Results data, the age-adjusted incidence rates of DCIS increased from 3.9% annually between 1973 and 1983 to 17.5% annually from 1983 to 1993. 2 This is an overall increase of 557%. This dramatic increase has been observed in both white and black women and in all age groups. It has been estimated that in 1993, 23,275 cases of DCIS were diagnosed in the United States and an estimated 9245 mastectomies were performed. 2 Approximately 4676 women who were 40 to 49 years old were diagnosed with DCIS, and approximately 1890 mastectomies were performed on women in the same age group. 2
This dramatic increase that has been found in the incidence of DCIS is probably attributable to increased use of screening mammography. Ernster et al 1 estimated that in 1992 15,500 excess cases of DCIS were diagnosed because of the use of screening mammography and approximately 7000 mastectomies were performed for mammographically detected disease. DCIS now makes up 20% to 40% of all breast cancers diagnosed at the initial screening mammogram. Data from the University of California, San Francisco Mobile Mammography Screening Program suggest that for 40-to 49-year-old women, DCIS made up 42.6% of cancers detected at an initial screening test. 2 Furthermore, published data suggest that the proportion of new breast cancer cases that are DCIS remains relatively constant with age. In contrast, the incidence of invasive cancer increases significantly with age. This suggests that the higher incidence of DCIS observed among younger women is not because DCIS is more common in younger women but is because of the lower incidence of invasive disease in this age group. 2
Prevalence of DCIS: Data From Autopsy Series
Researchers have performed several autopsy studies in an attempt to determine the baseline prevalence of DCIS in women who were not diagnosed with breast cancer. 3-1l In these studies, the median prevalence of