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The paper discusses changes in the structure of the classification, criteria for the diagnosis of lymphoid neoplasms in the 5th edition of the WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues (2022). Changes are presented regarding new nosological units, renaming and abolition of some previously existing ones. The importance of molecular genetic studies in the isolation of many lymphomas and the need to apply these studies in everyday clinical practice are emphasized. Lymphoid precancerous processes and lymphoid proliferations introduced into the Classification for the first time are considered.

The article reviews the changes in the structure of classification, diagnostic criteria for myeloid and histiocytic neoplasms in the 5 th edition of the WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues (2022). Information is presented regarding new nosological forms, renaming and abolition of some previously existing ones. The importance of molecular genetic studies in the isolation of myeloid and histiocytic neoplasms and the need to apply these studies in clinical practice are emphasized. Myeloid and histiocytic precancerous and proliferative processes, genetic tumor syndromes, introduced into the classification for the first time, are considered.

Background: Metagenomic studies in recent years have demonstrated that all tissues of the human body studied by genomic and transcriptomic sequencing methods, both in pathological processes and in normality, contain fragments of DNA and RNA from a variety of microorganisms. The composition of tissue microbiota and its relationship with development of pathological changes are still poorly understood, despite increasing number of studies in this area every year. In this study, gene expression of the lymph node microbiome in reactive follicular hyperplasia and follicular lymphoma was investigated., Objective: To study expression of lymph node microbiome genes in reactive follicular hyperplasia and follicular lymphoma., Material and Methods: The work included 38 biopsy samples of lymph nodes with follicular lymphoma of different cytological subtypes and 10 biopsy samples of lymph nodes with reactive follicular hyperplasia. Verification of diagnosis was carried out using standard histological, histochemical and immunohistochemical methods. Using sequencing method, the transcriptome was examined. Statistical analysis and data visualization were performed using the R programming language (version 4.2.1)., Results: Tumor lymph nodes are characterized by large Simpson and Shannon alpha diversity values (p-value = 0.026465 and p-value = 0.007122, respectively). Two clusters were discovered, characterized by different levels of relative abundance of microorganisms., Conclusion: It has been proven that diversity of microorganisms present in tumor tissue and their number are statistically significantly higher than corresponding indicators in the lymph nodes with follicular hyperplasia.

The first documented case of mitochondrial neurogastrointestinal encephalomyopathy was described in 1962 by R. Luft. The variety and am-biguity of the clinical manifestations of the disease complicate its early diagnosis and treatment. The first clinical manifestations of the disease are associated with the pathology of the gastrointestinal tract. Low alertness and insufficient awareness of doctors delays the timely diagnosis of mitochondrial neurogastrointestinal encephalomyopathy. The aim of the work is to increase the alertness and awareness of narrow specialties about the possibility of differential diagnosis of an extremely rare detected disease on the base of our clinical observation.

Kikuchi-Fujimoto disease (KFD) is a rare disease that is clinically manifested mainly by fever and lymphadenopathy. KFD was originally believed to occur primarily in East Asia women, this disease was subsequently described in all ethnic groups worldwide. The important differential diagnostic feature of KFD is the detection of CD123-expressing plasmocytoid dendritic cells (PDCs) in the tissue of the affected lymph node. The standard immunohistochemical staining method has sufficient sensitivity and specificity to detect CD123, but it gives no way of judging the possible phenotypic heterogeneity of cells with CD123 expression., Objective: To identify the phenotypic heterogeneity of CD123-expressing cells in the affected lymph nodes in patients with KFD by a sequential immunoperoxidase labeling and erasing (SIMPLE) method., Material and Methods: Excision biopsies of lymph nodes were examined in 3 patients with KFD. After an immunohistochemical reaction using a single antibody, the tissue specimen was digitized with a Pannoramic 250 Flash III scanner (3DHISTECH, Hungary), then the cover glass was removed from the section, the specimen was hydrated and placed in a specialized buffer. Then the following primary antibody was applied to the washed tissue specimen and further immunohistochemical reaction and scanning were performed. As a result, each tissue specimen was sequentially stained in reactions with 4 antibodies. The microphotographs of specimens stained in a reaction with anti-CD123 antibody showed positive cells for their identification in the Pannoramic Viewer program (3DHISTECH, Hungary) on the remaining microphotographs displaying the expression of the other 3 markers. The selected fields of view were exported to a JPG format., Results: Assessing the co-expression of the antigens CD123, MNDA, CD68, and TCL1A detected 4 CD123+ cell subpopulations: No. 1. CD68+/ MNDA+/ TCL1A+; No. 2. CD68+/ MNDA+/ TCL1A-; No. 3. CD68+/ MNDA-/ TCL1A+; No. 4. CD68-/ MNDA-/ TCL1A+., Conclusion: SIMPLE has shown the phenotypic heterogeneity of CD123-positive cells (some of them may be PDCs) and could identify 4 immunophenotypically distinct subpopulations in the affected lymph nodes in patients with KFD. Further investigations are needed to define the role of subpopulations in the pathogenesis of KFD and other diseases.

Neural network analysis of digital copies of histological micropreparations is one of the methods used to standardize quantitative continuous data. PD-L1 (22C3) biomarker expression in metastatic non-small cell lung carcinomas without mutations in the EGFR, ALK, and ROS1 genes serves as an indication for the use of pembrolizumab for the first-line therapy., Objective: To quantify PD-L1 biomarker expression in non-small cell lung carcinomas using the neural network analysis of digital copies of histological micropreparations., Material and Methods: Immunohistochemical study of PD-L1 (22C3) expression was performed on 96 non-small cell lung carcinoma biopsy specimens. The digital copies of histological micropreparations were processed by the QuPath software neural network analysis module., Results: The neural network analysis module segmented tumor, stroma, and artifacts in the micropreparations, showing a sufficient level of agreement with a visual assessment. Digital image analysis quantified stained tumor cells in the high PD-L1 expression group and showed 96% agreement rate versus visual assessment. However, the group of tumors without PD-L1 expression versus visual assessment showed a low (58%) agreement rate., Conclusion: The neural network analysis algorithm is applicable to the study of digital copies of histological micropreparations containing tumor, stroma, and artifacts. The algorithm allows for quantitative immunohistochemical assessment of PD-L1 expression in tumor cells. The algorithm can quantify the immunohistochemically detected expression of PD-L1 in tumor cells.

The paper is devoted to changes in the 4 th edition of the WHO classification of lymphoid tumors in the 2017 revision, to the principles of the structure and features of the classification. It discusses changes in the identification of new clinical and morphological categories and in the abolition of some previously existing ones. New information about lymphoid tumors, their immunophenotypic and molecular characteristics of classification importance are briefly outlined. The absolute need for molecular genetic studies for the diagnosis of certain lymphoproliferative diseases is underlined. The characteristics of lymphoid pretumor states are given.

Objective: To assess the applicability of imported tissue-marking dyes and the samples of experimental dyes and decorative acrylic paints to mark the resection margins of a surgical specimen., Material and Methods: Three sets of tissue-marking dyes: 2 imported sets and 1 experimental set, each containing red, orange, yellow, green, blue, purple, and black dyes, and a set of decorative acrylic paints containing black, blue, light blue, green, yellow, ocher, orange, magenta, and purple dyes. The experimental dyes and imported ones were used to mark tonsillar fragments obtained at tonsillectomy. The set of experimental dyes and that of decorative acrylic paints were used to stain the fragments of autopsy specimens (the skeletal muscles, pancreas, and large bowel). The tissues obtained at autopsy were marked before and after fixation in 40% formalin for 30 min and 24 hours. The specimens were subjected to standard tissue processing. Paraffin blocks were cut into 5-μm sections that were stained with hematoxylin and eosin. To estimate resection margin marking, each specimen was examined by 7 researchers who independently assessed the covering ability of a dye and its color in the paraffin block and microslides., Results: All researchers correctly identified purple, black, and green colors from the three sets of dyes in the surgical tonsillar specimen. When examining the autopsy specimens, all the experts correctly recognized magenta and green decorative acrylic paints and black and blue experimental dyes. The time of fixation and the type of tissue did not affect the color of a dye in the paraffin block and tissue specimen., Conclusion: Some of experimental dyes and decorative acrylic paints are highly competitive with imported tissue-marking dyes in their characteristics, are correctly recognized in the block and tissue specimen under a microscope, and can be proposed to mark the resection margins of the examined tissues.

Mantle cell lymphoma (MCL) has a heterogeneous clinical course and is mainly an aggressive B cell non-Hodgkin lymphoma; however, there are some indolent cases The Ki-67 index, defined by the percentage of Ki-67-positive lymphoma cells on histopathological slides, has been shown to be a very powerful prognostic biomarker. The pathology panel of the European MCL Network evaluated methods to assess the Ki-67 index including stringent counting, digital image analysis, and estimation by eyeballing. Counting of 2 × 500 lymphoma cells is the gold standard to assess the Ki-67 index since this value has been shown to predict survival in prospective randomized trials of the European MCL Network. Estimation by eyeballing and digital image analysis showed a poor concordance with the gold standard (concordance correlation coefficients [CCC] between 0.29 and 0.61 for eyeballing and CCC of 0.24 and 0.37 for two methods of digital image analysis, respectively). Counting a reduced number of lymphoma cells (2 × 100 cells) showed high interobserver agreement (CCC = 0.74). Pitfalls of the Ki-67 index are discussed and guidelines and recommendations for assessing the Ki-67 index in MCL are given.