Overview of the Current Definition of Ductal Carcinoma in Situ

Donald L. Weaver, MD; University of Vermont

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The definition of DCIS has evolved over time. The term carcinoma in situ was coined in the 1930s when pathologists established that intraductal carcinoma existed, but it was a subtype of typical, invasive carcinoma. From the 1950s to the 1970s, this thinking evolved significantly, as pathologists became better able to distinguish pure DCIS. In the 1970s, electron microscopy demonstrated that DCIS has cytoplasmic extensions through gaps in the basement membrane. This observation created controversy and confusion with respect to defining a non-invasive form of breast cancer. In the late 1970s to early 1980s, lower grade, noncomedo forms of DCIS were widely recognized. In the 1980s, DCIS was established as a distinct clinical-pathological entity and it was determined that not all DCIS needed to be treated by mastectomy. The single most important scientific advance for detecting DCIS was the introduction of mammography, which provided physicians the ability to identify calcifications indicative of lesions within the breast tissue that might represent cancer.

Only certain cells within the duct, known as progenitor cells, proliferate and differentiate into normal luminal and basal epithelial cells. It is not clear whether cancer arises only from the undifferentiated progenitor cells or may also arise from partially or fully differentiated epithelial cells.

The defining features of DCIS include:

• Malignant cytologic features (monomorphic or pleomorphic);
• Involvement of two duct cross-sections and/or the sum of the duct diameters involved in the lesion greater than 2 mm;
• All malignant cells must be confined to the basement membrane inside the duct;
• Single cells or angular clusters must not be present outside specialized stroma of the lobule; and

DCIS can be graded as low (good prognosis; well differentiated) to high (poor prognosis; poorly differentiated) based on the nuclear grade and amount of necrosis. Because low-grade DCIS and atypical ductal hyperplasia (ADH) have similar cytology and genetic abnormalities, volume helps distinguish the two. In high-grade DCIS where architecture may be complex, the absence of the basal myoepithelial layer indicates invasion.

Because of the change in definitions and perception, it is difficult to retrospectively examine DCIS in historical medical records. Additionally, grading schemes differ, margin status may be recorded variably or not at all, and volume documentation is poor. Even when slides are examined, differences in diagnostic sampling may lead to incorrect assessment of the extent, grade, and margin status of DCIS. Data are heterogeneous and of variable quality, and even with the introduction of College of American Pathologist (CAP) checklists, this trend may continue in the future.