Patient selection, histological classification and clinical findings
Registered patients were retrieved retrospectively from the Department of Pathology, Fukuoka University, from 1990 to 2019. Histological classification was performed according to the WHO classification in 2017 [2. 23]. Forty-seven nodal PTCL-NOS, 39 AITL and seven F-TCL patients were selected in this study. Criteria of small, medium and large tumour cell sizes were in accordance with those of mantle cells, centrocytes and centroblasts in lymphoid follicles. Among PTCL-NOS, the large cell group was characterised by diffusely non-cohesive proliferation of ≥ 50% large lymphoma cells with distinct nucleoli. The small cell group consisted of predominantly medium-sized (n = 7) and small cell (n = 20) lymphomas. The small cell group included 10 cases of Lennert lymphoma. TFH+ PTCL was defined by more than two TFH markers and lacking AITL features. Diffuse infiltrate of atypical CD4+ lymphocytes with more than two TFH markers, clear cell nests, prominent proliferation of high endothelial venules and CD21+ dendritic cell nests were main criteria of AITL. Scattered and patchy infiltrates of plasma cells and eosinophils were additional criteria of AITL. Follicular TCL was definite by nodular proliferation of atypical TFH+ lymphocytes and lacing AITL features. Corresponding medical records were reviewed to obtain clinical information, including Ann Arbor stage, treatments and overall survival.
Histology, immunohistology, and detection of EBV-encoded RNA
Excised tissue specimens were fixed in 10% formalin to generate formalin-fixed and paraffin embedded (FFPE) wax samples and stained with haematoxylin and eosin. Immunohistology was performed on the tumour tissues using the Leica Bond III automated stainer (Leica Biosystems, Buffalo Grove, IL, USA). Antibodies against the following proteins were used: CD3 (PS1, Leica, Newcastle, UK), CD4 (4B12, Leica), CD8 (C81/44B, Leica), CD10 (56C6, Leica), CD25 (interleukin 2 receptor [IL2R], 4C9, Leica), CD30 (BerH2, DakoCytomation, Glostrup, Denmark), PD-1 (NAT105, Abcam, Cambridge, MA), CXCL13 (BLC, R&D, Minneapolis, MN), BCL6 (LN22, Leica), CMYC (Y69, Abcam), MIB1 (MIB1, Dako), PD-L1 (E1L3N, Cell Signaling, Danvers, MA), CD20 (L26, Nichirei, Tokyo), and CD21 (1F8, Dako). Tumour cell counts were semi-quantitatively calculated by two pathologists and percentages of antibody-positive cells were determined (0%, 5%, and 10%–100% in 10% increments) in over five high power fields [12]. For the four TFH markers (PD-1, BCL6, CD10 and CXCL13), samples with ≥ 20% labelling of the tumour cells were considered positive [4]. Expression of CMYC, MIB1 and PD-L1 in ≥ 50% atypical lymphoid cells was estimated as positive (n+) [17], and staining intensity of PD-L1 in histiocytes and dendritic cells was scored as follows: R0 (no staining), R1+ (a few cells to < 5%), R2+ (≥ 5% – < 20%) and R3+ (≥ 20%). For the other antibodies, samples with ≥ 30% labelling of the tumour cells were considered positive. The presence of EBV infection was determined by in situ hybridisation of EBV-encoded RNA (EBERs)+ nuclear signals (BOND EBER probe, Leica)
Quantitative real time polymerase chain reaction
Total RNAs were extracted from FFPE tumour specimens of 42 patients using the NucleoSpin total RNA FFPEXS (Macherey-Nagel, Duren, Germany), according to the manufacturer’s instructions, on a real-time PCR machine (Mini OpticonTM, BioRad, Hercules, CA, USA). All samples were tested for expression of CMYC (assay ID: Hs00905030_m1, amplicon size 87 bp) [12]. In addition, samples were analysed for expression of GUSB (Hs99999908_m1), TBP (Hs00427620_m1), and ABL1 (Hs00245443_m1), which were used for normalisation in the final analysis.
Detection of RHOA G17V mutation by Sanger sequencing
DNA samples from FFPE tumour tissue were extracted using a GenElute™ Mammalian DNA Miniprep Kit (Sigma-Aldrich, St. Louis, MO, USA). Detection of RHOA G17V mutation and wild type were assessed by allele-specific PCR. For RHOA amplification, PCR was performed with AmpliTaq gold (Thermo Fisher Scientific, Waltham, MA, USA) using 40 ng genomic DNA, 0.3 μM primers, and 2 μL AmpliTaq gold master mix. A PCR-amplified product of 244 bp, including the codon for the 17th amino-acid, was obtained in 53 patients, and direct sequencing of these products was performed. The coding DNA position 50G>T mutation of the RHOA gene predicted change of the wild-type G (Gly) to the mutant type V (Val) [22].
Statistical analysis
All pairwise comparisons of categorised variables between the histological groups and types of PTCL were performed using the χ2 or Fisher’s exact test. Of the 93 recruited patients, 87 PTCL patients were examined for clinical outcome. Outcome was determined by calculating cumulative survival from time of diagnosis to date of the last follow up or death. Overall survival (OS) curves were generated using the Kaplan–Meier method with log-rank tests, and analysed by the proportional Hazard model. A p value < 0.05 was considered statistically significant. Analyses were performed using software JMP 10 (SAS Institute, Cary, NC, USA).