CD27 and neoplasm: Based on Panel 2 (CD27, CD138, IgG, and CK19) mIF staining, plasma cells and tumor cells were defined as IgG+ plasma cells (CD138+, CD27+/–, IgG+); IgG− plasma cells (CD138+, CD27+/–, IgG−); IgG+ tumor cells (CK19+, IgG+); and IgG− tumor cells (CK19+, IgG−) (Figure 5a,b).