Introduction. The use of invasive methods for diagnosing primary diffuse large B-cell lymphoma of the central nervous system (PDLBCL CNS) and primary vitreoretinal lymphoma (PVRL) is often associated with the development of severe neurological deficits and disability of patients. A promising direction in the diagnosis of PDLBCL CNS and PVRL is the use of non-invasive approaches based on molecular genetic methods for the determination of mutations in the MYD88 gene in the cerebrospinal fluid (CSF), vitreous fluid (VF) and free circulating tumor DNA (cfDNA) in blood serum. Aim: to present the potential of non-invasive diagnosis of PDLBCL CNS and PVRL. Main findings. The study included 6 patients (4 - PDLBCL CNS, 2 - PVRL). The average age was 64 (54-75) years. Despite increased cytosis in the CSF in all 4 patients with PDLBCL CNS, the tumor population was determined by flow cytometry in only half of the cases. According to a molecular genetic study, mutations in the MYD88 gene with an allelic load from 2.5% to 15% were detected in the genomic DNA of the CSF of all patients. In 2 patients with PVRL, mutations in the MYD88 gene were detected in VF with an allelic load of 4.2% and 6.6%, which was the only confirmation of the diagnosis. Currently, 5 patients have completed the treatment program and 1 is undergoing therapy. All 5 patients are in complete remission (CR) of the disease with follow-up periods from 1 to 8 months.

Introduction. Currently, Ibrutinib is one of the most effective drugs for relapsed and refractory chronic lymphocytic leukemia treatment. In most patients with CLL, ibrutinib causes persistent remissions, but in some patients the disease progresses. Ibrutinib resistance in most cases is associated with the C481S mutation, which corresponds to the c.1441T>A and c.1442G>C substitutions in the BTK gene, however, other variants also exist.Aim — to evaluate variable allele fraction of the BTK gene mutations in patients with relapsed chronic lymphocytic leukemia using the in-house allele-specific real-time PCR test.Materials and methods. The study included material from 102 cases: 39 CLL patients with disease progression on ibrutinib therapy, 24 CLL patients with disease progression on the FCR/FCR-lite protocols, and 38 CLL treatment-naive patients. The control group included 118 patients with non-neoplastic hematological diseases.Results. Using in-house using AS-PCR, we detected the c.1442G>C mutation in 20 out of 39 CLL patients with progression on ibrutinib therapy. Mutation c.1442G>T was detected in 2 patients. In a single patient, two mutations were detected simultaneously: c.1441T>A and c.1442G>C. Another single patient had a combination of three mutations: c.1442G>C, c.1442G>T and c.1442G>A. In 15 patients with progression on ibrutinib therapy, mutations in the BTK gene were not detected. In treatment-naive CLL patients, in the group treated with FCR/FCR-lite regimens, and in the control group of patients with nonneoplastic diseases, mutations in the BTK gene were not detected.Conclusion. Variable allele fraction of exon 15 BTK gene mutations in the patients with CLL progression was successfully determined using in-house AS-PCR test: 50 % of patients had one mutation, 5 % had two mutations, and 2.5 % had three mutations in the BTK gene. Timely detection of these mutations before clinical recurrence may facilitate effective treatment strategy. Since clinical manifestations of ibrutinib resistance appear after an average of 1–2 years, we suggest monitoring BTK mutation load every 3 months in patients with CLL before relapse during treatment with ibrutinib.

APL is the rarest form of acute myelogenous leukemia.Advances in the treatment of APL have transformed this disease from a condition associated with significant morbidity and mortality to one with an excellent outcome.We present a case of a 68-year-old male who presented with delirium at the Saint Louis Hospital in July 2016.He was diagnosed with AML and achieved complete remission on day 10 of the first consolidation by ATRA/ATO.A neurologic examination revealed fluctuating delirium with temporospatial disorientation.During exploration, he was unable to focus.Cranial nerves were fully intact, and muscle strength was 5/5 throughout.He was hyper-reflexive on the right side compared with the left, and his toes were curled bilaterally, with no tremors or dysmetria.After a few hours, the patient experienced a sudden neurological deterioration with coma Glasgow 3.He was transferred to the intensive care unit.Consolidation therapy was discontinued due to neurological degradation.A Total CT scan was normal, and MRI showed no T2 signal changes.A lumbar puncture showed a WBC count 1, glucose 4.46 mmol/l, and protein 0.54.CSF cultures were negative, and a normal EEG.Investigations revealed a WBC of 6.64/mm 3 , hemoglobin 8.6 g/l, blasts 0%, normal electrolytes, bacteriology, and virology were negatives.The level of arsenic in the urine was 11394 ug/L (N 0 -50 ug/L).The results of CNS investigations were normal.Thus, the focus of the differential diagnosis shifted towards a primary psychiatric disorder.Based on consultation with the psychiatrist, there was no basis for a psychiatric decompression of thymic origin.The patient was diagnosed with an iatrogenic confusional syndrome caused by arsenic toxicity.The patient was treated with succimer 600 mg TID for 10 days with monitoring of the level of arsenic in the urine.On day 4 of treatment with succimer, the patient had a slow favorable resolution of symptoms with a clear improvement of temporal-spatial disorientation and nocturnal agitation.Arsenic trioxide is not known to cause encephalopathic side effects in leukemia patients.However, the side effect observed in this patient were reversible.The patient was treated with idarubicin + ATRA per guidelines and achieved complete remission.

Chronic lymphocytic leukemia (CLL) is one of the most common B-cell malignancies in Western countries. IGHV mutational status is the most important prognostic factor for this disease. CLL is characterized by an extreme narrowing of the IGHV genes repertoire and the existence of subgroups of quasi-identical stereotyped antigenic receptors (SAR). Some of these subgroups have already been identified as independent prognostic factors for CLL. Here, we report the frequencies of TP53, NOTCH1, and SF3B1 gene mutations and chromosomal aberrations assessed by NGS and FISH in 152 CLL patients with the most common SAR in Russia. We noted these lesions to be much more common in patients with certain SAR than average in CLL. The profile of these aberrations differs between the subgroups of SAR, despite the similarity of their structure. For most of these subgroups mutations prevailed in a single gene, except for CLL#5 with all three genes affected by mutations. It should be noted that our data concerning the mutation frequency in some SAR groups differ from that obtained previously, which could be due to the population differences between patient cohorts. The research in this area should be important for better understanding the pathogenesis of CLL and therapy optimization.

Background. Tumor cell proliferation in acute myeloid leukemia (AML) may manifest with high leukocyte counts. In our work, we evaluate the association of high leukocyte counts with individual mutations, as well as their total contribution to the development of leukocytosis in AML. The results obtained should improve our understanding of pathogenic mechanisms leading to the leukocytosis in AML. Aim. To study the genetic landscape of AML with leukocytosis. Materials and methods. The laboratory data of 214 AML patients admitted to the National Medical Research Center for Hematology (Moscow) from 2010 to 2022 were retrospectively examined. Real-time PCR, capillary electrophoresis and NGS (next generation sequencing) methods were used to detect mutations of FLT3, NPM1, CEBPA, IDH1/2, DNMT3A, TET2 genes, and CBFB::MYH11, RUNX1::RUNX1T1 chimeric gene transcripts. Results. Mutations of the FLT3 gene (odds ratio 5.45; p < 0.0001), inv(16)/ CBFB::MYH11 (odds ratio 10.03; p = 0.0009) are most associated with leukocyte counts higher than 30 × 10 9 / L in the debut of AML. Translocation t(8;21) /RUNX1::RUNX1T1 and adverse cytogenetic aberrations, such as -5/del(5q); -7 / del(7q); -17 / abn(17p), complex and monosomic karyotype were significantly associated with leukocyte counts lower than 30 × 10 9 / L at the time of disease manifestation (p < 0.0001). In the group of patients with intermediate cytogenetic risk bearing only IDH1/2, DNMT3A , and TET2 gene mutations, leukocyte counts at AML debut were significantly lower, whereas the most pronounced leukocytosis was observed in patients with a combination of driver mutations with IDH1/2, DNMT3A , and TET 2 gene mutations or FLT3, NPM1 , and CEBPA gene mutations. Conclusion. In addition to the individual effect of certain genetic lesions and cytogenetic aberrations on the proliferative potential of tumor cells, there is a total contribution of various types of genetic events to the development of leukocytosis in AML. High leukocyte counts at the time of AML manifestation in patients with intermediate cytogenetic risk can serve as an indirect marker of the presence of a large number of genetic aberrations with a combination of IDH1/2, DNMT3A , and TET2 gene mutations or FLT3, NPM1 , and CEBPA gene mutations.

Aim. To determine the incidence and prognostic value of mutations in exon 16 of EZH2 as well as those of polymorphism с.1582-21А>G (rs2072407) in EZH2 in patients with follicular lymphoma (FL) grades 1–3А in relation to morphologic and cytogenetic tumor characteristics. Materials & Methods. The prospective cohort study conducted by the National Research Center for Hematology from January 2017 to April 2021 enrolled 80 patients with newly diagnosed FL grades 1/2 and 3А. The median follow-up was 53 months. Molecular and cytogenetic analyses were based on biopsy samples of lymph nodes obtained before chemotherapy. The mutation status of exon 16 in EZH2 and the presence of intronic polymorphism rs2072407 in EZH2 were examined by Sanger sequencing method. Translocation t(14;18)(q32;q21) was detected by karyotyping or FISH. Results. Mutations in exon 16 of EZH2 (mutEZH2) were identified in 10/80 (13 %) patients. All patients showed missense mutation in codon 646 of EZH2. Translocation t(14;18) was detected in 45/80 (56 %) cases. Poor outcome in the cohort with no t(14;18) was observed 3 times more often than in the group of patients with t(14;18) (p = 0.0001). The presence of t(14;18) was associated with favorable prognosis irrespective of either the mutation status of exon 16 in EZH2 or the FL grade. The analysis of the polymorphism rs2072407 status yielded the following genotypes: AA in 24 % (n = 19), AG in 42 % (n = 34), and GG in 34 % (n = 27) of cases. The variants АА and AG were associated with higher risk of death (hazard ratio 2.9; 95% confidence interval 1.2–10.6; p = 0.01), whereas the genotype GG was associated with wtEZH2 (10 % vs. 37 %) and favorable prognosis (p = 0.065). Conclusion. Significant biological markers for favorable prognosis in FL appeared to be the presence of t(14;18)(q32;q21) and GG genotype of polymorphism rs2072407 in EZH2. The previously identified prognostic factors (grade 3А, bulky tumor lesions > 6 cm, Ki-67 > 35 %, and a short interval between symptom onset and chemotherapy start) were incorporated into a new unified personalized predictive (index PPI) FL model by supplementing it with two additional biological markers: the presence of t(14;18)(q32;q21) and GG genotype of polymorphism rs2072407. This approach may increase the prognostic value of the new personalized design which will provide the basis for risk-adapted algorithms for FL treatment.

Background:NPM1 gene mutations are found in 30% of acute myeloid leukemia (AML) cases. It is a reliable marker for the evaluation of therapy outcome and minimal residual disease (MRD) monitoring. The most often mutations are 4bp insertions in exon 12, affecting 2 functionally important tryptophan residues (W288 and W290) in the C-terminal region of nucleophosmin and causing a frameshift. As a result, a leucine-rich motif (L-xxx-V-xx-V-x-L) is formed, which is a signal sequence for protein export from the nucleus to the cytoplasm. Commonly NPM1 gene mutations are detected by fragment analysis (FA) of PCR fragment of 12 exon for the presence of 4bp insert. Alternatively, allele-specific polymerase chain reaction (AS-PCR) to detect inserts belonging to the A, B, or D type (representing up to 90% of all inserts) is used. However, about 10% remaining cases are non-standard inserts and intron polymorphisms that require more precise evaluation. Aims: Evaluation of diverse approaches for efficient NPM1 gene mutation analysis and their robustness for the diagnostics. Methods: The study included 80 DNA samples from AML patients admitted to the National Research Center for Hematology in 2019-2021 that were positive for NPM1 gene mutations detected by FA performed with the Nanophor-5 genetic analyzer (Synthol, Russia). The type of insert was assessed by AC-PCR. Samples in doubt were evaluated by targeted next-generation sequencing (NGS) on MySeq (Illumina, USA). Results: In 62 out of 80 samples, the type of insert (A, B, or D) was reliably determined by AS-PCR. In 9 cases type of insert was not detected. In further 9 cases, amplification ΔCt between wild-type and mutant allele was out of reliable range. These 18 samples were examined by NGS, and 2 out of 18 showed an intron deletion, which, presumably, does not affect the function of the protein, but leads to the appearance of an additional peak on FA. In 16 out of 18 samples, non-standard inserts were detected (Table 1). Type A inserts were found in 48 out of 78 cases (61.5%), type B - in 2 out of 78 (4.5%), and type D - 15.4% (12 out of 78). We have detected atypical inserts in 16 out of 78 cases (20.5%), which is more than reported in the literature. 14 out of 16 atypical inserts result in a leucine-rich motif, as do standard inserts. In 4 out of 16 cases, one of the 2 functionally important tryptophan residues was retained (W280), therefore possibly conserving nuclear localization signal. The effect of partial preservation of the nucleolar localization of nucleophosmin on prognosis in AML has not been studied yet. Image:Summary/Conclusion: FA is still a golden standard for screening NPM1 gene mutations in AML. AS-PCR could be effectively used for monitoring cases with standard inserts. However, NGS greatly facilitates non-standard inserts identification, appropriate allele-specific primers design for MRD analysis, and avoiding false-positive FA results for cases with intron localization of the insert.

Background: Ibrutinib is highly effective for CLL treatment. It inactivates Bruton’s tyrosine kinase (BTK) by forming a covalent bond in the enzyme catalytic domain at position C481. Ibrutinib resistance in 50-80% of cases is associated with the C481S mutation in exon 15 of the BTK gene (Ahn et al, 2017; Woyach et al, 2017), which corresponds to the c.1441T>A and c.1442G>C substitutions, still, other variants of gene mutations at this position are also reported. Monitoring allelic load of the BTK gene mutations conferring resistance to ibrutinib is extremely important for studying the mechanism of CLL progression during treatment with BTK inhibitors. Aims: Development and validation of a real-time AS-PCR approach for assessing the relative allelic load of BTK gene mutations in Russian CLL patients treated with ibrutinib. Methods: The study included DNA samples from 101 patients (pts) with CLL: 39 pts with disease progression on ibrutinib therapy (67% male, median age 64.5 years; 33% female, median age 64 years); 24 pts with progression after FCR or FCR-lite therapy (62% men, median age 62 years; 38% women, median age 67 years); 38 primary pts (76% men, median age 64 years; 24% women, median age 60 years). 89 pts with non-neoplastic hematological diseases were selected as control samples. All DNA samples were tested using a real-time AS-PCR with the following primers and probes: c.1441T (5’-CTGAGTACATGGCCAATGGCT-3’); c.1441T>A (5’-CTGAGTACATGGCCAATGGCA-3’); c.1442G (5’-CTGAGTACATGGCCAATGGCTG-3’); c.1442G>C (5’-CTGAGTACATGGCCAATGGCTC-3’); c.1442G>A (5’-TGAGTACATGGCCAATGGCAA-3’); c.1442G>T (5’-TGAGTACATGGCCAATGGGTT-3’); REV (5’-CTGCTACTTCCACCCCATCA-3’); Probe (5’-R&G-TGCTAGAGATGTGCAAGGATGTCTGTGAAG-RTQ1-3’). All DNA samples from pts treated with ibrutinib were analyzed by NGS on a MiSeq genetic analyzer (Illumina, USA). Results: Initially, AS-PCR was performed only for the most common mutations c.1441T>A and c.1442G>C, however, after NGS of the BTK gene in pts with progression during ibrutinib therapy, other options were added to the test system. Using AS-PCR, out of 39 Russian pts with CLL progressing on the background of ibrutinib therapy, a single c.1442G>C mutation was detected in 19 (48.7%) pts (including 3 samples with a low mutant load); 2 (5.1%) had a single mutation c.1442G>T (C481F). In 1 (2.6%) patient, two mutations were detected simultaneously: c.1441T>A and c.1442G>C, and in another 1 (2.6%) patient, 3 mutations were detected simultaneously: c.1442G>C, c. 1442G>T (C481F) and c.1442G>A (C481Y). No mutations in the BTK gene were found in 16 (41%) Russian pts. Table 1 shows a good agreement between the results of NGS with AS-PCR when sequencing the BTK gene in this group of pts, both in identifying the type of mutation and in determining the relative mutational load. To determine the presence or absence of mutations in the studied samples, the amplification curves and Ct values of the normal and mutant alleles were compared. Thus, mutations in the BTK gene leading to an amino acid substitution at position C481 were found in 59% of Russian pts with CLL treated with ibrutinib. In groups of pts with CLL without prior treatment, after FCR/FCR-lite regimens, and in the control group of pts with non-neoplastic diseases, no mutations were found. Image:Summary/Conclusion: AS-PCR protocol effective for the analysis of the BTK gene mutations leading to an amino acid substitution at position C481 has been developed and validated. Prospective studies of low burden BTK mutations in the pathogenesis of relapse in CLL patients treated with BTK inhibitors have been started using this approach.

TP53 plays a key role in almost all cellular processes. Mutations in this gene are found in most types of neoplasms. Among hematological malignancies, TP53 lesions are the most actively studied in CLL, although available data for other lymphomas remains limited.To study the frequency and diversity of TP53 mutations in Russian patients with B-cell lymphomas.The study included 145 DNA samples from patients with B-cell lymphomas: 53 patients with DLBCL, 47 patients with MCL, and 45 patients with FL, 16 of whom experienced transformation to DLBCL. Mutations in TP53 (exons 4-10) in most samples were detected using NGS (138 patients) or Sanger sequencing (7 patients). The clinical significance of detected variants was assessed using the Seshat online tool based on the UMD TP53 database.TP53 mutations were detected in 24 DLBCL patients (45.4%), 21 of which were missense mutations, 2 were splicing site mutations, and 1 was an insertion. Sixteen variants were identified as (probably) pathogenic, and 8 mutations were of unclear significance. Del17p was simultaneously detected in 7 patients with TP53 mutations (of 11 examined). In MCL patients, mutations were found in 19 cases (40%). Eighteen were missense mutations, and 1 was a splicing mutation. Sixteen variants were identified as (probably) pathogenic, and 3 were variants of unclear significance. Chromosome 17 abnormalities were found in 7 MCL patients with TP53 mutations of 11 studied. In FL patients, TP53 mutations were detected in 12 cases (26.7%). Eight were missense mutations, 2 were nonsense mutations, 1 was a splicing mutation, and 1 was a deletion. Nine variants were recognized as (probably) pathogenic, and 2 were variants of unclear significance. Only 1 patient of 6 examined had del17p.The frequency of TP53 mutations in our cohort of patients with B-cell lymphomas was significantly higher than the frequency reported for other cohorts. This bias may be due to differences in patient selection. We are planning further studies examining the type of mutations, allelic loads, and combinations with other chromosome 17 lesions in association with the disease course.

Background: The TP53 gene plays a key role in cell cycle control, DNA repair, initiation of apoptosis, and other critical cellular processes. Mutations of this gene are found in almost all types of malignant neoplasms and the vast majority of cases are associated with poor prognosis. Among hematological malignancies, TP53 gene lesions are most actively studied in CLL, while for other lymphomas fewer data are available so far. Aims: To study the frequency, variation, and allelic load of TP53 mutations in Russian patients with B-cell lymphomas. Methods: The study included 145 DNA samples from patients with B-cell lymphomas admitted to the National Medical Research Center for Hematology (Moscow, Russia) in 2020-2021: 53 patients with DLBCL (29F, 24M, age 25-87 years, median 54 years), 47 patients with MCL (17F, 30M, age 42-73 years, median 59 years) and 45 patients with FL (28F, 17M, age 30-72 years, median 49 years), 16 of them with transformation to DLBCL. Mutations in the TP53 gene (exons 4-10) in most samples were detected using NGS according to Pavlova et al., or Sanger sequencing (7 patients). The clinical significance of the detected variants was assessed using the Seshat online tool based on the UMD TP53 database. Results: TP53 gene mutations were detected in 24 DLBCL patients (45.4%). Out of them were found 21 missense mutations (2 cases in the “hot spots” p.R249M and p.R282W and 2 cases in the same position p.G266), 2 splicing site mutations, and 1 insertion. Also, 16 variants were identified as (likely) pathogenic, 13 of which had a mutation load (VAF) greater than 15%. Of the 8 mutations of unclear significance, 4 had a VAF<10%. Del17p was simultaneously detected in 7 patients with TP53 mutations (out of 11 examined). In the MCL patients mutations were found in 19 cases (40%). 18 of them were missense mutations (4 in the “hot spot” p.R248 and 2 in the same position p.V173) and 1 splicing mutation. 16 variants were identified as (likely) pathogenic and had a VAF>14%. All 3 variants of unclear significance were minor. Chromosome 17 abnormalities were found in 7 MCL patients with TP53 mutations out of 11 studied. In the FL patients, TP53 mutations were detected in 12 cases (26.7%). Out of 8 missense mutations, 4 were in hotspots p.R175H, p.R248Q, p.R249M, p.R273H. Also in this group 2 nonsense mutations, 1 splicing mutation, and 1 deletion were observed. Of the 9 variants recognized as (likely) pathogenic, only 1 was minor, as were 2 variants of unclear significance. Only 1 patient with TP53 mutation out of 6 examined had del17p. All results are presented in Table 1. Image:Summary/Conclusion: The frequency of mutations in the TP53 gene in patients with B-cell lymphomas in our sample is significantly higher than according to the literature data. One can explain this bias by patient selection. A significant portion of DLBCL and FL patients admitted to our center in the state of progression or relapse. Most MCL cases were primary, however, MCL patients with advanced stages of the disease are more often admitted to the National Medical Research Center for Hematology. At the same time, the occurrence of “hot spots” mutations in MCL and FL is also higher than expected. Further studies concerning the type of mutations, their allelic load, and their combination with 17th chromosome lesions in association with disease course are on the way.

Background: Follicular lymphoma (FL) is characterized by clinical and morphological heterogeneity. It is based on the pathogenetic mechanisms of the development of tumor cells. The identification and assessment of risk factors associated with the course of the disease and treatment outcome in FL is an important task, as it allows to evaluate and predict the effectiveness of therapy.

Background About 30% of cases of CLL express highly homologous “stereotype” antigenic receptors (SARs) which can be assigned to different subsets. Several SARs have already been identified as independent prognostic factors for CLL (CLL#1, CLL#2, CLL#8 are associated with extremely aggressive course of the disease, CLL#4 - indolent). It is suggested that different SARs may also associate with the occurrence of certain genetic lesions. Aim To evaluate the frequency of cytogenetic aberrations and TP53, NOTCH1 gene mutations in Russian patients of CLL#1 subset, the most common CLL subset in Russia. Methods We tested 20 CLL patients with SAR CLL#1 for NOTCH1 (34 exon) and TP53 (2-11 exons) gene mutations by fragment analysis and NGS sequencing. FISH study for the presence of 17p13/TP53, 11q23/ATM, 13q14 deletions and 12 trisomy also was done. Results TP53 gene mutations were detected in 5 patients (25%); all mutations were described as pathogenic. Also, in 5 (25%) patients, NOTCH1 gene mutations were detected. Simultaneous mutations in the NOTCH1 and TP53 genes were detected in two patients (10%). Deletion 17p13 was found in 4 patients (27%) from 15 evaluated. Three patients simultaneously had a mutation in the TP53 and del17p13 gene; in all these cases, the mutated TP53 allele burden was higher than 40%. In 5 of 11 patients, 11q23 deletion was found (45%). There were no cases with the simultaneous occurrence of del11q23 and del17p13 or mutations in the TP53 gene. In one patient, both del11q23 and a mutation in the NOTCH1 were found. One patient showed a 13q14 biallelic deletion (simultaneously with del17p13 and mut TP53). Trisomy of the 12th chromosome was not detected. Conclusion Our data show that in Russian patients with CLL#1 subset, genetic lesions are much more common than in patients with CLL in general. That is mostly consistent with earlier European studies. Further studies of genetic lesions in CLL#1 and other subsets are required for better understanding of CLL pathogenesis and improving diagnostics and therapy. About 30% of cases of CLL express highly homologous “stereotype” antigenic receptors (SARs) which can be assigned to different subsets. Several SARs have already been identified as independent prognostic factors for CLL (CLL#1, CLL#2, CLL#8 are associated with extremely aggressive course of the disease, CLL#4 - indolent). It is suggested that different SARs may also associate with the occurrence of certain genetic lesions. To evaluate the frequency of cytogenetic aberrations and TP53, NOTCH1 gene mutations in Russian patients of CLL#1 subset, the most common CLL subset in Russia. We tested 20 CLL patients with SAR CLL#1 for NOTCH1 (34 exon) and TP53 (2-11 exons) gene mutations by fragment analysis and NGS sequencing. FISH study for the presence of 17p13/TP53, 11q23/ATM, 13q14 deletions and 12 trisomy also was done. TP53 gene mutations were detected in 5 patients (25%); all mutations were described as pathogenic. Also, in 5 (25%) patients, NOTCH1 gene mutations were detected. Simultaneous mutations in the NOTCH1 and TP53 genes were detected in two patients (10%). Deletion 17p13 was found in 4 patients (27%) from 15 evaluated. Three patients simultaneously had a mutation in the TP53 and del17p13 gene; in all these cases, the mutated TP53 allele burden was higher than 40%. In 5 of 11 patients, 11q23 deletion was found (45%). There were no cases with the simultaneous occurrence of del11q23 and del17p13 or mutations in the TP53 gene. In one patient, both del11q23 and a mutation in the NOTCH1 were found. One patient showed a 13q14 biallelic deletion (simultaneously with del17p13 and mut TP53). Trisomy of the 12th chromosome was not detected. Our data show that in Russian patients with CLL#1 subset, genetic lesions are much more common than in patients with CLL in general. That is mostly consistent with earlier European studies. Further studies of genetic lesions in CLL#1 and other subsets are required for better understanding of CLL pathogenesis and improving diagnostics and therapy.