Ductal carcinoma in situ ( DCIS) is a group of heterogeneous lesions genetically, morphologically, and biologically. Recently, breast epithelium in the terminal ductal lobular unit has been sub-classified based on the expression of several cytokeratin markers as stem cells (CK5/6+), luminal cells (CK8, CK18 +), and basal cells ( CK14, CK17 +). In this study we describe the relationship between DCIS of different nuclear grades ( non-high grade and high grade) and these cell origin markers. Fifty-three cases of non-high grade and 46 cases of high grade DCIS were selected, and representative sections from each case were stained with antibodies to these cytokeratin markers. High grade DCIS showed significantly higher rates of expression with stem and basal cell markers compared with non-high grade DCIS ( p < 0.05). The majority of DCIS, both high grade and non-high grade, expressed luminal cell markers ( 67% to 91%) and single type of cell origin marker (72% to 87%). High-grade DCIS more frequently co-expressed all three types of cell origin markers compared with non-high grade DCIS ( p < 0.05). In summary, a subset of high grade DCIS frequently rises from stem or/and basal cell populations; the subset is associated with poor prognosis in invasive breast carcinoma. Thus, these markers may be used to identify a potentially more aggressive subgroup of breast carcinoma at its pre-invasive stage ( DCIS), and to manage it accordingly. Second, most DCIS express luminal cell markers, suggesting that malignant transformation occurs relatively late along the cell differentiation pathway, contrary to the traditional belief that most neoplasms arise from a more primitive stem cell population. Third, the majority of DCIS exclusively express one type of progenitor marker, indicating that in most incidences they may arise from a single progenitor population. Last, triple expression of all types of cell origin marker is frequently associated with high grade DCIS, suggesting that more complicated pathways are involved in these more aggressive lesions. Further studies are needed to delineate the relationships of cell origin markers in DCIS and invasive carcinoma to the clinical outcome.