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The paper presents new molecular data, the principles of the classification of myeloid neoplasms, and criteria for their diagnosis according to the new edition of the WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues, 2017. Current concepts of clonal hematopoiesis and models of clonal evolution are presented to characterize the common features of the molecular pathogenesis of myeloid neoplasms. There are new data and general principles of diagnosis of myeloid neoplasms: Ph-negative myeloproliferative diseases, myelodysplastic syndromes, myeloid/lymphoid neoplasms with eosinophilia and rearrangements of PDGFRA, PDGFRB, FGFR1, and PCM1-JAK2, diseases from the group of myelodysplastic/myeloproliferative diseases. Emphasis is laid on the possibilities and limitations of pathological differential diagnosis when a pathologist examines bone marrow trepanobiopsy specimens in his/her routine work.Представлены новые молекулярные данные, принципы классификации и критерии диагностики миелоидных неоплазий согласно новой редакции Классификации ВОЗ опухолей гемопоэтической и лимфоидной ткани (2017). Изложены современные представления о клональном гемопоэзе и модели клональной эволюции, позволяющие охарактеризовать общие черты молекулярного патогенеза миелоидных неоплазий. Рассматриваются новые сведения и общие принципы диагностики миелоидных неоплазий: Ph-негативных миелопролиферативных заболеваний, миелодиспластических синдромов, миелоидных/лимфоидных опухолей с эозинофилией и реаранжировками PDGFRA, PDGFRB, FGFR1, PCM1-JAK2, заболеваний из группы миелодиспластических/миелопролиферативных заболеваний. Обращается внимание на возможности и ограничения патоморфологической дифференциальной диагностики при исследовании трепанобиоптатов костного мозга в условиях повседневной работы врача-патологоанатома.

The paper presents the results of estimating the quality of immunohistochemical (IHC) staining in 36 pathologic laboratories of the Russian Federation. The results of IHC stains were assessed in 17 markers (CD3, CD5, CDIO, CD15, CD20, CD23, CD30, Bcl2, Bcl6, Pax5, TdT, Mum1, Cyclin D1, Ki-67, Kappa, Lambda, ALK), which are frequently used in the diagnosis of lymphoproliferative diseases, in the sections of specially formed tissue matrices. The study conducted in most participating laboratories has revealed the considerable IHC staining technology flaws that can critically affect the quality of diagnosis of lymphoproliferative diseases; the diagnostic capacities of some participating laboratories are inconsistent with the solved problems for a number of key antibodies being unavailable.

The paper deals how to improve the differential diagnosis of lymphomas by an immunohistochemical study. The introduction of DNA chips for the study of the gene expression profile in different types of lymphomas has created conditions for the emergence of the new class of protein antibodies--target genes. New immunohistochemical algorithms are being developed; the antibodies, the products of cytogenetic anomalies, chimeric genes emerge, which gives rise to prospects for the wide introduction of immunohistochemistry into pathologoanatomic practice. From the new diagnostic points of view, some types of lymphomas, as given in the September 2008 WHO classification of hematopoietic and lymphoid tissue tumors, are considered.

Principles of morphological diagnosis of anaplastic large-cell lymphoma (ALCL) are considered, several its variants are distinguished: classic (32 cases), small-cell (4 cases), rich in granulocytes (2 cases) and lymphohistiocytic (1 case). ALK expression was variable: 93% at the age up to 20, 60% at the age from 20 to 40 years, none at the age 40 years and older. Morphological similarities between ALCL, classic variants of Hodgkin's lymphoma, variants of diffuse large B-cell lymphoma may require immunohistochemical investigation the criteria of which are suggested.

Morphological and immunophenotypical features of Hodgkin's lymphoma with lymphoid predominance are described: a variant with nodular lymphoid predominance (NLPHL) and variants of large-cell lymphoma including mediastinal large B-cell lymphoma, diffuse large B-cell lymphoma rich with T-cells and/or histiocytes. In view of the fact that these lymphomas enter so-called "gray zone" criteria for immunohistochemical differential diagnosis are suggested.

Stomach MALT-lymphomas have a specific feature of clinical behaviour and prognosis, this being reason to differentiate it from others gastric lymphoma's variants. 75 cases of gastric MALT-lymphomas having "classical" morphological features with polymorphic tumour infiltration. We described the only case of MALToma in our series characterised by a strong marker tendency of monoclonal plasmocytic differentiation (including plasmoblasts) with 'signet-ring' cells, Dutcher and Russel bodies using morphological, histochemical and immunohistochemical methods. We suppose this case to be MALT lymphoma with Mot's cell differentiation.

Histiocytic sarcoma consisting of phagocyting histiocytes is a rare variant of histiocytic sarcoma. It is hard to detect because of its similarity with large cell lymphomas, in particular with anaplastic large cell lymphoma. Histological and immunohistochemical findings are presented. Differential diagnosis with tumours of hematopoietic and non-hematopoietic nature is described.

MALT gastric lymphoma presents difficulties for morphological diagnosis as it is represented by neoplastic elements having morphology of mature cells. 75 MALT-lymphomas of the stomach with polymorphous tumour infiltrate are reported. The infiltrate was analyzed by cell composition, cell atypia, the presence of lymphoepithelial lesions (LEL) and lymphoid follicles, blast cells and "blast" LEL. Immunohistochemistry may be necessary for diagnosis when clear-cut morphological characteristics are lacking.

A topical problem of differential diagnosis of nodular lymphoid predominance of Hodgkin's lymphoma and classical variant rich in lymphocytes is discussed. Main morphological diagnostic criteria are considered on the basis of the authors' observations and literature data. Immunological characteristics of two variants of Hodgkin's lymphoma with lymphoid predominance are reviewed.

The results are available of clinical, morphological, cytological and immunological investigations of orbital lymphomas and lymphomas of appendages of the eye. Malignant lymphoma was detected in 17 patients and reactive lymphoid hyperplasia in 3 patients. All the malignant lymphomas had B-cell phenotype. By cell composition, MALT-lymphoma is more polymorphic than lymphoma from mantle zone cells and lymphoma from small lymphocytes and centro follicular lymphoma. The conjunctive is affected primarily with lymphoma from marginal zone cells or mantle zone cells. As a rule, this is a primary local lesion. Other variants of orbital lymphoma and lymphoma of the eye appendages develop more often as secondary lesions in systemic disease and are characterized by more aggressive course. The key in differential diagnosis of reactive lymphoid hyperplasia and small cells lymphomas is immunophenotyping, especially at initial stages of the tumor process.

A rare case of aggressive ovarian tumor in a 38-year-old female is described. Cytological diagnosis of the intraoperative smears was difficult because of the presence of the epithelial and non-epithelial components. The latter consisted of two types: spindle cells and roundish undifferentiated cells with multinuclear forms. Histologically, it was a malignant mesodermal (Mullerian) mixed tumor. Round mesenchymal cells expressed desmin and vimentin while spindle cells expressed myoglobin. Non-epithelial component was verified as leiomyosarcoma and rhabdomyosarcoma. Cells of the epithelial component expressed cytokeratins and epithelial membrane antigen.