Ductal carcinoma in situ (DCIS) is a preinvasive clinical diagnosis that lies in the continuum between epithelial atypia and invasive cancer. Although it has been recognized and treated for almost three decades, much remains controversial about this disease and its optimal treatment. The incidence of DCIS has increased significantly since it was first described, largely as a consequence of widespread mammographic screening. Accordingly the presentation pattern has changed from a predominantly palpable lesion to one whose first indication is that of an incidentally discovered mammographic abnormality on routine screening examination. Because DCIS is a preinvasive condition with heterogenous potential for invasion, there remains ongoing debate over whether the current treatment recommendations represent overtreatment of some DCIS which may have never resulted in clinical consequences during a patient’s lifetime. This chapter reviews the epidemiology, diagnosis, and treatment of DCIS as well as some future directions for clinical management of the disease.
BACKGROUND AND EPIDEMIOLOGY
The incidence of DCIS has increased over 500% in the last 30 years, with over 50,000 women diagnosed annually.1 Data collected by the National Cancer Institute’s Breast Cancer Surveillance Consortium (BCSC) estimates that one case of DCIS is detected for approximately every 1300 screening mammography examinations performed.2 The incidence rate varies by age, ranging from approximately 1 in every 1800 mammograms among women aged 40 to 49 years to 1 in every 935 mammograms among women aged 70 to 84 years. The overall prevalence of screen-detected breast cancers diagnosed as DCIS was significantly higher in the younger, compared to the older age group (28.2%: age 40 to 49; 16% to 20%: age 60 to 84 years). With current treatment options, breast cancer mortality from DCIS is less than 2% at 10 years. The primary objectives in treatment of DCIS are to prevent local recurrence of DCIS or progression to invasive carcinoma, and to maintain the high rates of disease-free survival.3
By diagnosing and treating this burden of DCIS, a commensurate reduction in the incidence of early invasive cancer would be expected; however, this has not been reflected in the observed incidence rates for breast cancer.4 Moreover, the prevalence of undiagnosed DCIS is substantial and may be seen in up to 14% of women in routine autopsy series, confirming that many patients with unrecognized DCIS die with the disease and not of it.5
The risk factors for DCIS do not differ from those for invasive breast cancer, and it is widely accepted that DCIS is a precursor lesion to invasive breast cancer. However not all DCIS may have the ability to progress to invasion.6 By examining tumors that contain both an invasive and noninvasive component, studies have demonstrated that the expression of tumor markers is highly similar in both components.7,8 This suggests that genomics likely influence grade, rather than invasiveness. Despite significant advances in our understanding of cancer ...