Pax 5 sp34

Immunohistochemical stains were performed on formalin-fixed, paraffin-embedded (FFPE) tissue sections following routine
procedures on a Ventana Benchmark automated stainer (Roche Ventana Medical Systems, Tucson, AZ), using the antibodies against CD20
(L26, Roche Diagnostics), CD3 (2GV6, Ventana), CD79a (SP18, Roche Diagnostics), PAX-5 (SP34, Roche Diagnostics), LMP1 (CS
1–4, Dako), EBNA2 (PE2, Abcam), (CD138 (B-838, Roche Diagnostics), kappa (rabbit, Roche Diagnostics), lambda (rabbit,
Roche Diagnostics), CD38 (SPC32, Vector), MUM-1 (MRQ-43, Roche Diagnostics), Ki-67 (MIB-1, Dako), IgG (rabbit, Dako), IgM (rabbit,
Dako), and IgA (rabbit, Dako). Epstein-Barr virus-encoded small RNA (EBER) in situ hybridization was performed as previously
described ^{13 (link)}.

All cases were examined in formalin-fixed paraffin-embedded (FFPE) tissue sections. Immunohistochemical stains were performed using an automated immunostainer (Benchmark/Ultra, Roche) according to the company’s protocols, with minor modifications. Antigen retrieval was performed using a pressure cooker “Tender Cooker” (Nordicware, Minneapolis, MN) with citrate buffer or directly on the immunostainer. Antibodies included: CD3 (2GV6, Roche), CD20 (L26, 1:1,000; Dako, Carpinteria, CA), CD79a (SP18, Roche), PAX5 (SP34, Roche), Mum1 (MRQ-43, Roche), CD138 (B-B4, 1:200, Dako), Kappa (1:25,000; Dako), Lambda (1:10,000; Dako), IgA (1:20,000; Dako), IgD (1:500; Dako), IgG (1:12,000; Dako), IgG4 (1:1,000; Abcam), IgM (1:10,000; Dako), Ki-67 (Ki-67, 1: 100, Dako), CD56 (MRQ-42, Roche), LMP1 (CS.1–4, 1:400, Dako), and MYC (Y69,1:100, Abcam). All Roche antibodies are pre-diluted.
The standard cutoff of MYC≥40% was used to define MYC overexpression in PBL. In contrast, the percent of cells staining positive for MYC was documented in both EBV-positive plasmacytoma and EBV-negative plasmacytoma as no cutoff has been established for plasmacytoma.