FREM2 and ductal breast carcinoma in situ: According to the analysis of cellular localization, 11 core upregulated DEGs (e.g., FREM2 and NOD2) and 17 core downregulated DEGs (e.g., PTPRK and CAV1) were associated with the cell surface, suggesting that the characteristics of cell surface proteins of the DCIS cells could help distinguish DCIS cells from normal cells.