PAX5 and neoplasm: The pathological diagnosis was CLL/SLL. Immunohistochemistry (Figure 1) revealed that the tumor cells were positive for CD20, CD79a, PAX5, CD5, CD23, MUM-1 (partially), and BCL-2, background T cells were positive CD3, some helper T cells were positive for CD4, BCL6, PD-1, and CXCL13, some T cells were positive for CD8, with approximately 40% of cells positive for Ki-67.