Megakaryocytes, erythropoietic and granulopoietic cells express CAL2 antibody in myeloproliferative neoplasms carrying CALR gene mutations.

Testing for the CALR mutation is included in the updated WHO criteria for essential thrombocythaemia (ET) and primary myelofibrosis (PMF). We report on the application of the CAL2 monoclonal antibody, raised against the mutated CALR gene to myeloid cases. The immunostain was used on 116 acute myeloid leukaemias (AML) and 66 myeloproliferative neoplasms (MPN) or myelodysplastic syndromes/myeloproliferative neoplasms (MDS/MPN). None of AML cases was stained by the CAL2 antibody, while 20/66 MPNs and MDS/MPNs appeared positive. Fourteen of the latter cases were studied by molecular techniques, and all showed aberrations of the CALR gene. In addition, CAL2 positivity was found in some small-sized elements besides megakaryocytes. By double staining, these elements corresponded to small megakaryocytes as well as both erythroid and myeloid precursors. This finding suggests possible occurrence of CALR gene abnormalities in a stem cell.

Molecular switch from MYC to MYCN expression in MYC protein negative Burkitt lymphoma cases.

MYC is the most altered oncogene in human cancer, and belongs to a large family of genes, including MYCN and MYCL. Recently, while assessing the degree of correlation between MYC gene rearrangement and MYC protein expression in aggressive B-cell lymphomas, we observed few Burkitt lymphoma (BL) cases lacking MYC protein expression despite the translocation involving the MYC gene. Therefore, in the present study we aimed to better characterize such cases. Our results identified two sub-groups of MYC protein negative BL: one lacking detectable MYC protein expression but presenting MYCN mRNA and protein expression; the second characterized by the lack of both MYC and MYCN proteins but showing MYC mRNA. Interestingly, the two sub-groups presented a different pattern of SNVs affecting MYC gene family members that may induce the switch from MYC to MYCN. Particulary, MYCN-expressing cases show MYCN SNVs at interaction interface that stabilize the protein associated with loss-of-function of MYC. This finding highlights MYCN as a reliable diagnostic marker in such cases. Nevertheless, due to the overlapping clinic, morphology and immunohistochemistry (apart for MYC versus MYCN protein expression) of both sub-groups, the described cases represent bona fide BL according to the current criteria of the World Health Organization.

Problems and pitfalls in grading of bone marrow fibrosis, collagen deposition and osteosclerosis - a consensus-based study.

AIMS: In the era of potentially disease-modifying agents such as Janus kinase inhibitors, accurate grading and differentiation of bone marrow (BM) fibrosis has become more relevant to assess staging of disease and therapeutic effects. However, different fibrosis grading models have been used in the past without uniformity, including the proposal by the World Health Organization. Current scoring systems are based only on reticulin fibrosis. Therefore, additional assessment of collagen and the grade of osteosclerosis appear to be essential to discriminate all components of the complex BM fibrous matrix. METHODS AND RESULTS: We evaluated problems and pitfalls regarding staining techniques and the interpretation of reticulin fibrosis on a total of 352 samples. Furthermore, we propose a minor modification of the current grading and separate scoring for collagen deposition and osteosclerosis. Reproducibility of gradings was tested among 11 haematopathologists in a blinded assessment. Overall, the inter-rater reliability of all three grading systems ranged between 0.898 and 0.926. CONCLUSIONS: A standardized assessment of BM fibrosis with differentiation between reticulin, collagen and osteosclerosis is recommended to evaluate the various components of the fibrous matrix which may be delinked after therapy. In this regard, quality of staining and application of laboratory standards enable a highly reproducible scoring.

Histopathological features and their prognostic impact in nodular lymphocyte-predominant Hodgkin lymphoma--a matched pair analysis from the German Hodgkin Study Group (GHSG).

Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is a rare lymphoma entity. We performed a matched-pair analysis to evaluate the prognostic impact of several histopathological features in this distinct Hodgkin lymphoma subtype. Lymph node samples of NLPHL patients were tested for CD15, IgD, phosphorylated STAT6, ICOS and Epstein-Barr virus status of the malignant lymphocyte-predominant cells as well as epithelioid cell clusters and activated T cells in the microenvironment. None of these features was associated with a particular clinical outcome. However, patients presenting with epithelioid cell clusters showed a non-significant trend towards a lower relapse rate, justifying further evaluation of this marker.

The prognostic impact of variant histology in nodular lymphocyte-predominant Hodgkin lymphoma: a report from the German Hodgkin Study Group (GHSG).

Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) accounts for approximately 5% of all Hodgkin lymphoma cases. The aim of this study was to evaluate the prognostic implication of histopathologic NLPHL variants. Biopsies of 423 NLPHL patients treated within 9 prospective clinical trials performed by the German Hodgkin Study Group were classified as tumor cell-rich cases (n = 10), typical NLPHL (n = 308), or histopathologic variants (n = 105). Histopathologic variants were characterized by the presence of lymphoma cells outside the B-cell nodules or B-cell depletion of the microenvironment. Compared with typical NLPHL, histopathologic variants were associated with advanced disease (29.5% vs 14.6%, P = .0012) and a higher relapse rate (18.1% vs 6.5% at 5 years, P = .0009). Variant histology represented an independent prognostic factor (odds ratio = 2.955) in a multivariate model of progression/relapse. A prognostic score, including the risk factors variant histopathologic growth pattern, low serum albumin, and male gender, was derived from this model and allowed the definition of 3 distinct risk groups. NLPHL patients presenting with histopathologic variants have a poorer outcome compared with those showing typical histology. The newly developed prognostic score combining histologic and clinical features allows allocating NLPHL patients to defined risk groups.

Nodal reactive and neoplastic proliferation of monocytoid and marginal zone B cells: an immunoarchitectural and molecular study highlighting the relevance of IRTA1 and T-bet as positive markers.

AIMS: Marginal zone B cells (MZCs) and monocytoid B cells (MBCs) appear to be related lymphoid cells that take part in reactive and neoplastic marginal zone proliferations. These lesions are not yet well characterized, and the aim of this study was to find better diagnostic criteria for them. METHODS AND RESULTS: We analysed 60 nodal lesions with MBC and/or MZC proliferation for their morphological, immunophenotypic, molecular genetic and IG gene rearrangement features. On the basis of the results of the rearrangement assay and immunoglobulin light chain restriction, the lesions were divided into reactive and neoplastic groups. Among the neoplastic lesions, polymorphic and monomorphic subgroups emerged. All reactive lesions had morphological features of the polymorphic subgroup. By immunohistochemistry, IRTA1 and/or T-bet expression was found in all reactive lesions and in 90% of neoplastic lesions. CONCLUSIONS: IRTA1 and T-bet are positive markers for the identification of MZC/MBC proliferations, and thus for the diagnosis of nodal marginal zone lymphoma (NMZL). Polymorphic and monomorphic subgroups of NMZL could be distinguished. Most morphological and immunophenotypic patterns in reactive and neoplastic nodal expansions of MZCs and MBCs overlapped. Therefore, PCR clonality assay of the immunoglobulin heavy and light chain gene loci is the most reliable method for their differentiation.

Is Hodgkin lymphoma just another B-cell lymphoma?

Hodgkin disease was the first defined lymphoid neoplasm. For many decades it was regarded as a disease separate from non-Hodgkin lymphoma. However, recent studies have shown that the dysplastic cells of Hodgkin lymphoma (HL) are monoclonal B cells. This finding raised again the question "Is HL just another B-cell lymphoma?" This article reviews the different aspects of HL and B-cell non-Hodgkin lymphoma (B-NHL), concluding that-despite the same cell of origin-fundamental differences exist in morphology, cellular composition, immunophenotype, activation or inhibition of transcription factors, epigenetics, and clinical behavior. These findings lead us to conclude that HL and B-NHLs should stay as two separate categories.