IRF4 and neoplasm: Initial immunostains showed that tumor cells were positive for CD45RB, CD20, CD23 (positive in a subset of tumor cells but no FDC meshwork seen), CD10, BCL6, CD30 (positive in a subset of tumor cells), and MUM1, but negative for CK AE1/AE3, CK7, CK20, TTF1, CD68, chromogranin, synaptophysin, p40, CD3, CD5, BCL1, and BCL2, indicating a preliminary diagnosis of DLBCL, GCB type.