We herein present an overview of the upcoming 5^thedition of the World Health Organization Classification of Haematolymphoid Tumours focussing on lymphoid neoplasms. Myeloid and histiocytic neoplasms will be presented in a separate accompanying article. Besides listing the entities of the classification, we highlight and explain changes from the revised 4^thedition. These include reorganization of entities by a hierarchical system as is adopted throughout the 5^thedition of the WHO classification of tumours of all organ systems, modification of nomenclature for some entities, revision of diagnostic criteria or subtypes, deletion of certain entities, and introduction of new entities, as well as inclusion of tumour-like lesions, mesenchymal lesions specific to lymph node and spleen, and germline predisposition syndromes associated with the lymphoid neoplasms.

The normal counterpart of the neoplastic B cells in Burkitt lymphoma (BL) is still unclear. Based on immunoglobulin gene rearrangement studies, some authors suggest an origin from germinal center cells and others from memory B cells. However, most of these studies rely on cell lines or on a small series of cases. To help clarify the cell of origin of BL, semi-nested polymerase chain reaction (PCR) was performed to amplify the VDJ rearrangements of the immunoglobulin heavy chain (VH) genes, and the resultant amplificates were sequenced for comparison with known germline VH segments. The results of this approach revealed that all cases (15 endemic BL [eBL], 10 sporadic BL [sBL], and 6 AIDS-related BL) harbor mutated VH genes, with different mutation ranges among the 3 types of BL. The eBL and AIDS-related forms showed considerably higher mutation rates than the sBL form (5.1%, 5.4%, and 1.5%, respectively). The mutations in eBL and AIDS-related BL also showed signs of antigen selection, whereas no signs of antigen selection were found in sBL. Finally, after subcloning the amplificates, sequence analysis revealed no signs of ongoing mutations in any of the cases analyzed. Given that one of the main differences between eBL and AIDS-related BL on the one hand and sBL on the other hand is the association with Epstein-Barr virus (EBV), we compared EBV-positive and EBV-negative BLs independently of their geographic origin and HIV status. The differences in the number of somatic mutations and antigen selection were even more evident when this approach was used. According to our molecular results, it appears that EBV-positive and EBV-negative BL may originate from 2 distinct subsets of B cells, pointing to a particular role for the germinal-center reaction in the pathogenesis of these tumors. The different types of C-MYC translocation reported in BL may also be related to the different stages of B-cell maturation.

Burkitt lymphoma (BL) is classified into 3 clinical subsets: endemic, sporadic, and immunodeficiency-associated BL. So far, possible differences in their gene expression profiles (GEPs) have not been investigated. We studied GEPs of BL subtypes, other B-cell lymphomas, and B lymphocytes; first, we found that BL is a unique molecular entity, distinct from other B-cell malignancies. Indeed, by unsupervised analysis all BLs clearly clustered apart of other lymphomas. Second, we found that BL subtypes presented slight differences in GEPs. Particularly, they differed for genes involved in cell cycle control, B-cell receptor signaling, and tumor necrosis factor/nuclear factor κB pathways. Notably, by reverse engineering, we found that endemic and sporadic BLs diverged for genes dependent on RBL2 activity. Furthermore, we found that all BLs were intimately related to germinal center cells, differing from them for molecules involved in cell proliferation, immune response, and signal transduction. Finally, to validate GEP, we applied immunohistochemistry to a large panel of cases and showed that RBL2 can cooperate with MYC in inducing a neoplastic phenotype in vitro and in vivo. In conclusion, our study provided substantial insights on the pathobiology of BLs, by offering novel evidences that may be relevant for its classification and possibly future treatment.

Summary: Approximately 30 000 cases of non‐Hodgkin lymphoma (NHL) occur in the equatorial belt of Africa each year. Apart from the fact that Burkitt lymphoma (BL) is very common among children and adolescents in Africa and that an epidemic of human immunodeficiency virus (HIV) infection is currently ongoing in this part of the world, very little is known about lymphomas in Africa. This review provides information regarding the current infrastructure for diagnostics in sub‐Saharan Africa. The results on the diagnostic accuracy and on the distribution of different lymphoma subsets in sub‐Saharan Africa were based on a review undertaken by a team of lymphoma experts on 159 fine needle aspirate samples and 467 histological samples during their visit to selected sub‐Saharan African centres is presented. Among children (<18 years of age), BL accounted for 82% of all NHL, and among adults, diffuse large B‐cell lymphoma accounted for 55% of all NHLs. Among adults, various lymphomas other than BL, including T‐cell lymphomas, were encountered. The review also discusses the current strategies of the International Network of Cancer Treatment and Research on improving the diagnostic standards and management of lymphoma patients and in acquiring reliable clinical and pathology data in sub‐Saharan Africa for fostering high‐quality translational research.

Purpose: BRAF mutations are grouped in activating RAS-independent signaling as monomers (class 1–V600E) or as dimers (class 2–codons 597/601), and RAS-dependent with impaired kinase activity (class 3–codons 594/596). Although clinical, pathologic, and molecular features of V600EBRAF-mutated metastatic colorectal cancer (mCRC) are well known, limited data are available from the two other classes.Experimental Design: Data from 117 patients with BRAF (92 class 1, 12 class 2, and 13 class 3)-mutated mCRC were collected. A total of 540 BRAF wt mCRCs were included as control. IHC profiling was performed to determine the consensus molecular subtypes (CMS), cytokeratin 7/20 profiles, tumor-infiltrating lymphocyte infiltration, and BM1/BM2 categorization. Overall survival (OS) and progression-free survival were evaluated by Kaplan–Meier and log-rank test.Results: Class 3 BRAF-mutated mCRC was more frequently left sided (P = 0.0028), pN0 (P = 0.0159), and without peritoneal metastases (P = 0.0176) compared with class 1, whereas class 2 cases were similar to class 1. Hazard ratio for OS, as compared with BRAF wt, was 2.38 [95% confidence interval (CI), 1.61–3.54] for class 1, 1.90 (95% CI, 0.85–4.26) for class 2, and 0.93 (95% CI, 0.51–1.69) for class 3 (P < 0.0001). Class 2 and 3 tumors were all assigned to CMS2-3. A higher median CD3/CD8-positive lymphocyte infiltration was observed in BRAF-mutated class 2 (P = 0.033) compared with class 3 cases.Conclusions: For the first time, different clinical and pathologic features and outcome data were reported according to the three BRAF mutation classes in mCRC. Specific targeted treatment strategies should be identified in the near future for such patients.