Epidemiology of DCIS
Karla Kerlikowske, MD;
University of California at San Francisco
Once rare, DCIS now comprises 20 percent of all breast cancers, with an estimated 60,000 new cases diagnosed in 2006. Diagnosis of DCIS has increased as a result of increasing use of screening mammography. The increase in DCIS diagnosis has paralleled the increase in mammography machines since 1980, with 1 in 1,300 screening examinations leading to a diagnosis of DCIS. Although DCIS diagnoses from 1983 to 2003 increased 500 percent, the number of cases being diagnosed each year has reached a plateau since the late 1990s.
Incidence of DCIS increases with age before decreasing again after the ages of 70 to 75. Incidence of DCIS is similar in white, black, and Asian women, but white women have a higher incidence of invasive cancer. The risk factors for DCIS are similar to that of invasive cancer and include a family history of breast cancer, nulliparity or late age at first birth, previous breast biopsy, and late age at menopause. No association with smoking, body mass index (BMI), alcohol consumption, or oral contraception has been found. However, postmenopausal hormone therapy does significantly increase the risk for DCIS as it increases the risk of invasive cancer. Mammographic density, as measured by the Breast Imaging Reporting and Data System (BI-RADS) categories, increases risk of DCIS, similar to that of invasive cancer, with women with dense breasts being at 2-3 fold higher risk than those with fatty breasts. Carriers of oncogenes BRCA1 and BRCA2 also are at increased risk of DCIS.
DCIS is most commonly diagnosed on mammography, with 80 to 85 percent of cases being initially identified in this manner. A core biopsy or needle localization and excisional biopsy are used for definitive diagnosis. Unfortunately, mammography cannot distinguish DCIS lesions that will be associated with subsequent tumor events from those that will not. There are no criteria that can consistently stratify women with DCIS into risk categories of those most likely to have a subsequent DCIS event, those likely to have a subsequent invasive event, and those likely to have no further tumor events. Thus, it is necessary to continue to investigate the natural history of DCIS and determine which DCIS lesions are associated with the highest risk of a subsequent tumor events.
Treatment of DCIS is relatively aggressive, with the majority of patients undergoing lumpectomy or lumpectomy combined with radiotherapy. The number of patients undergoing mastectomy for DCIS is decreasing and the number taking adjuvant tamoxifen is increasing. Fifteen percent of women diagnosed with DCIS will have a subsequent invasive event within 10 years. The percentage of women with DCIS dying of breast cancer is low at 1 to 2% 10 years after diagnosis.