The bispecific monoclonal antibody blinatumomab (CD19/CD3) is widely and successfully used to treat children with relapsed/refractory B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Advances have also led to the use of immunotherapy in children with primary BCP-ALL. This paper presents the effectiveness of a single blinatumomab course instead of consolidation chemotherapy and with short maintenance therapy in primary BCP-ALL patients. The study was approved by the Independent Ethics Committee and the Scientific Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. Between February 2020 and November 2022, 165 children with non-high-risk BCP-ALL (according to clinical stratification criteria defined in the study) were enrolled in the ALL-MB 2019 pilot study (NCT04723342). Patients received conventional risk-adapted induction therapy according to the ALL-MB 2015 protocol. Those who achieved complete morphological remission at the end of induction received 15 µg/m2/day of blinatumomab immediately after induction for 4 weeks, followed by 12 months of maintenance therapy. Minimal residual disease (MRD) was measured using multicolor flow cytometryat the end of induction, then immediately after blinatumomab course, and then four times during maintenance therapy at threemonth intervals. All 165 patients successfully completed induction therapy and achieved complete hematological remission. All had their MRD measured at the end of induction. One hundred thirty-six (82.2%) patients were MRD-negative, and the remaining 29 patients showed various levels of MRD positivity. MRD was assessed in all 164 patients who completed the blinatumomab course. One patient had blinatumomab discontinued due to acute neurotoxicity and was subsequently treated according to the intermediate-risk ALL-MB 2015 protocol. All but one patient achieved MRD negativity after blinatumomab course, regardless of MRD value at the end of induction. One adolescent girl with a high MRD level after induction remained MRD positive after blinatumomab course and further received high-risk therapy with allogeneic hematopoietic stem cell transplantation. At the time of analysis, 162 children had completed all therapy, including 12 months of maintenance. MRD was examined in 151 of them, and all were MRD negative. Over a 4-year study period with a median follow-up of 2.5 years, 10 relapses were registered: 4 in the standard-risk group and 6 in the intermediate-risk group. The 4-year event-free survival was 89.1 ± 3.7 % for all patients, 92.0 ± 4.2 % and 82.8 ± 8.1 % for the standard and intermediate risk groups, respectively. At the time of analysis, all patients were alive; no deaths were registered. Although the presented results are preliminary and more time is needed for definitive conclusions, a 4-week 15 µg/m2/day blinatumomab course immediately after induction followed by 12 months of maintenance therapy is effective in achieving and maintaining MRD negativity in children with non-high risk BCP-ALL. This study showed the fundamental possibility of treating ALL by combining immunotherapy with the bispecific monoclonal antibody blinatumomab with a significant chemotherapy reduction.

The achievement of clinical and hematological remission at the end of induction therapy is one of the key treatment response parameters in pediatric acute myeloid leukemia (AML). Besides conventional cytomorphological evaluation of bone marrow (BM) blast count, minimal residual disease (MRD) measurement has been widely applied in routine clinical practice in recent years. The aim of the study was to compare the results of flow cytometric MRD evaluation with the results of cytomorphological BM investigation when assessing the achievement of remission at the end of induction in children with AML. The study was approved by the Independent Ethics Committee and the Scientific Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. We analyzed BM samples obtained from 402 children with AML, who had been treated according to the AML-MRD-2018 protocol and undergone simultaneous cytometric and cytomorphological BM investigation at the end of induction. A myelogram count was performed on 500 nucleated cells per BM smear. MRD was measured by 10-color flow cytometry with the 0.1 % cut-off for reliable MRD-positivity. The threshold of 5 % blasts was used as the criterion of complete remission (CR). Overall concordance of the two methods was 83.3 % for the CR status confirmation: in 335 out of 402 patients, the presence or absence of CR was stated using both techniques. Half of the 67 discordant samples were obtained from patients with a significant monocytic component of the leukemic population: 14 (20.9 %) with AML M4 and 20 (29.9 %) with AML M5. Among all FAB subtypes, the highest concordance rate was noted in patients with M1 variant (91.7 %), while the worst comparability – in children with megakarioblastic leukemia (M7 type, 72.7 %). Failure to achieve CR by cytomorphology did not influence the outcome of the patients who achieved CR as confirmed by immunophenotyping. At the same time, for flow cytometric BM investigation, achieving MRD negativity (< 0.1%) was the most significant favorable outcome predictor even at this rather early stage. Moreover, relapse incidence in children who were in CR but MRD positive (≥ 0.1 %) was higher than in patients who did not achieve CR at the end of induction according to flow cytometry (MRD ≥ 5 %), especially in the intermediate-risk group. This difference can be explained by more intensive chemotherapy (FLAI instead of HAM cycle) given to patients who did not achieve CR at the end of induction, and patients in the intermediate-risk group were additionally re-stratified to a high-risk group with subsequent hematopoietic stem cell transplantation. Flow cytometric and cytomorphological BM examination for the CR status confirmation at the end of induction in children with AML demonstrated a relatively high concordance rate (83.3 %). CR achievement by cytomorphology does not influence final outcome, although for the flow cytometry conventional threshold of 5 % also seems inadequate. We can assume that the modification of therapy is also required for patients with MRD ≥ 0,1 % at this stage of treatment.

Children with acute lymphoblastic leukemia (ALL) and slow clearance of minimal residual disease (MRD) demonstrate a significantly worse outcome as compared to those with fast response to chemotherapy. Bispecific monoclonal antibody blinatumomab is the key drug for CD19-directed immunotherapy which opens wide opportunities for the elimination of MRD in patients with B-cell precursor ALL (BCP-ALL). Aim of the study – to evaluate the effectiveness of blinatumomab for MRD elimination in children with BCP-ALL and slow MRD clearance treated by the “ALL-MB 2015” protocol. The study was approved by the Independent Ethics Committee and the Scientific Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. Patients from the “ALL-MB 2015” trial who demonstrated slow MRD clearance at the end of induction were included in the current study. MRD monitoring was performed by multicolor flow cytometry modified with respect to possible CD19 loss during targeted treatment. Threshold of 0.001% was used for MRD positivity definition. Between February 2020 and August 2023, 228 children with de novo Ph-negative KMT2A-negative BCP-ALL were defined as slow MRD responders according to the criteria of the “Moscow-Berlin” group. Fifty of them were treated with blinatumomab because of slow MRD clearance. Blinatumomab course was given immediately after induction in 23 children, after Consolidation I – in 14 patients, after Consolidation II – in 11 patients, while two children received immunotherapy prior to maintenance. After completion of blinatumomab course, 23 patients continued protocol treatment, 21 received maintenance only, two were treated with high-risk blocks and four received hematopoietic stem cell transplantation. Only 2 of 50 (4.0 %) patients remained MRD-positive after completion of blinatumomab course. By the end of December 2023, only two adverse events were registered: one relapse and one remission death. Two-year event-free survival was 94.7 % (standard error 3.6 %), while cumulative incidence of relapse was 2.6 % (standard error 2.7 %). Outcome in these 50 patients was much better in comparison with 178 children with a slow MRD response who did not receive blinatumomab. The use of blinatumomab in children with de novo Ph-negative BCP-ALL with slow MRD clearance allows achieving MRD-negative remission in nearly all cases. Although a longer follow-up is necessary for the reliable conclusion of CD19-directed therapy effectiveness, the promising results are obtained in the current study in this unfavorable patient group.

Acute leukemias of ambiguous lineage (ALAL) are rare acute leukemias (AL) that exhibit specific features of more than one hematopoietic lineage or show no distinct evidence of lineage differentiation. Immunophenotyping plays a key role in the diagnosis and classification of ALAL. Despite the availability of diagnostic criteria for ALAL proposed by different expert groups, the accurate diagnosis of ALAL representing a rare and heterogeneous group of diseases remains a challenge. In this paper, we present a brief analysis of 97 pediatric ALAL cases. Such a large cohort of cases with ALAL (ALALs comprising less than 1 % of all pediatric AL) was obtained as a result of the centralized diagnosis of AL. With regard to the obtained results, we have developed the guidelines for the interpretation of the results of immunophenotyping in the diagnosis of ALAL and for the integration of findings from flow cytometry, cytomorphology and genetic testing for the accurate diagnosis and classification of this group of AL.

The aim of this work is to evaluate the informativity of the ultrasound (US) in detecting retinoblastoma (RB) and the local invasion of the tumor in children using modern multi-purpose ultrasound scanners. Materials and methods. This study included 108 patients (216 eyes) examined for suspected RB. RB was diagnosed in 91 patients, 60 children had unilateral tumor, 31 – bilateral tumor (122 eyes). In the remaining 17 children (20 eyes damaged), different non-tumor pathology of the eye was revealed. Among 122 eyes affected by RB, 51 were removed with subsequent histological examination. 27 eyes were removed before treatment, 24 – after chemotherapy. Results. In our study the informativity of ultrasound in detecting RB are: sensitivity – 98.4 %, specificity – 96.8 %, accuracy – 97.7 %. Sensitivity, specificity and accuracy in assessing tumor invasion to the anterior segment of the eye are 36.4 %, 95.0 % and 82.4 % respectively, to the vitreous body – 97.7 %, 100 % and 97.9 %, to the optic nerve – 54.5 %, 57.1 % and 54.9 %. Conclusion . US examination using linear transducers of 9–18 MHz is highly informative in detecting RB, however, some indicators of the effectiveness in assessing local invasion are not high enough, due to the technical possibilities of the method. One possible way to improve the informativity – to use deep sedation during US examination.

Introduction . Liver tumors account for 1.1 % of all newly diagnosed neoplasms in children. The rarity of this pathology causes difficulties in differential diagnosis. Currently, magnetic resonance imaging (MRI) is the main and most promising method for diagnosing liver diseases. In our work, we decided to quantify the data from this study. Purpose of the study – determination of the possibilities of quantitative assessment of multiparametric MRI data in the differential diagnosis of benign and malignant liver tumors in children. Material and methods . 133 patients with 307 liver lesions aged from 5 months to 20 years were examined. All patients underwent MRI on high-field MRI machines using an extracellular contrast agent, which included T2 weighted images with and without suppression of the signal from adipose tissue, diffusion-weighted images with automatic calculation of maps of the apparent diffusion coefficient (ADC), T1 weighted images with suppression of the signal from adipose tissue before and after the introduction of a contrast agent (in the arterial, portal, venous and delayed phases). Quantitative characteristics of changes in signal intensity in the lesion, intact liver parenchyma, spleen, kidney, aorta, and inferior vena cava (IVC) were obtained. To level the influence of external factors, we used not the absolute values of the signal intensity, but the ratios: lesion/intact liver parenchyma, lesion/kidney, lesion/aorta, lesion/spleen, lesion/IVC. For each lesion, 5 coefficients were calculated in each of the sequences, with the exception of patients (n = 4) after splenectomy, in whom 4 coefficients were calculated. In addition, for images obtained after the injection of a contrast agent, the ratios of the signal on post-contrast images to the native phase were calculated. Quantitative parameters such as the maximum size of the tumor, its volume and the age of the patient were included in the calculation. Tumors were represented by benign (n = 139) and malignant (n = 169) formations. The diagnosis of all malignant neoplasms and some benign ones was confirmed morphologically, benign ones – using MRI with intravenous contrast and dynamic observation. Results . A mathematical model was built: A = 1/(1+e -Z ), where Z = 6,25019 + 1,03132 × S + 1,30077 × P 2le/li – 0,00459 × DC le + 4,01375 × P 1le/a – 2,05533 × P art le/li – 2,55823 × P port le/k + 7,56980 × P del5 le/k – 15,91047 × P del5 le/a . The model is informative and statistically significant (p < 0.001). If A > 0.5, it should be considered that the studied focus is of a malignant nature, if A ≤ 0.5, the formation is benign. Model sensitivity and specificity were, respectively, 0.947 and 0.917. Conclusion . The mathematical model makes it possible to differentiate between malignant and benign formations with a high degree of informativeness, which is a priority task in detecting a mass formation in the liver.

Flow cell sorting is an advanced laboratory technique that combines the analytical capabilities of flow cytometry with the ability to isolate pure cell populations from heterogeneous samples. It has tremendous potential both for fundamental research and laboratory diagnosis. For example, the combination of cell sorting and molecular genetic studies can be used to clarify ambiguous results of acute leukemia immunophenotyping obtained both at diagnosis and during minimal residual disease monitoring. These guidelines are based on years of experience in incorporating cell sorting into the diagnostic and monitoring processes at the Leukemia Immunophenotyping Laboratory of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. They include methods used for the confirmation of flow cytometry data depending on the type of leukemia, the stage of a flow cytometry assay and previous therapy. They also describe cell sorting algorithms for disease diagnosis and the specifics of sample preparation for cell sorting in different molecular genetic studies.

Multicolor flow cytometry is now routinely used in laboratory practice for minimal residual disease (MRD) monitoring in B-cell precursor acute lymphoblastic leukemia (BCP-ALL). This article describes the methodology of MRD detection in BCP-ALL using flow cytometry as recommended by the Russian-Belarusian multicenter group for pediatric acute leukemia studies. This wellharmonized approach includes recommendations for the choice of monoclonal antibodies, sample preparation, cytometer setup, flow cytometry data analysis and interpretation as well as for reporting. These guidelines allow application of multicolor flow cytometry for MRD monitoring in BCP-ALL in children and adults both in local laboratories and in multicenter settings in prospective clinical trials.

malignant neoplasms (MNP). The frequency of PNS in MNP ranges from 1 to 20 % according to different authors. One of the manifestations of PNS is acne, which occurs against the background of malignant neoplasm due to hormonal disorders. The presented article describes a clinical case of a patient with a mixed germ cell tumor and metastases in the retroperitoneal lymph nodes. The germ cell tumor produced human beta-chorionic gonadotropin, which led to the development of acne as a PNS. Antitumor treatment (surgical removal of the tumor and polychemotherapy) normalized the levels of human beta-chorionic gonadotropin and serum testosterone, which in turn led to regression of acne without acne therapy.

Multicolor flow cytometry is now routinely used in laboratory practice for the minimal residual disease (MRD) monitoring in B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Wide application of CD19-directed immunotherapy leads to frequent loss of CD19 expression, that hampers significantly the flow cytometric MRD detection methodology. We developed an antibody panel and data analysis algorithm for multicolor flow cytometry, which is a reliable method for MRD detection in patients with BCP-ALL treated with CD19-directed therapy. We recommend a single-tube 11-color panel for MRD detection, which is adapted for the case of possible CD19 loss. Based on patterns of antigen expression changes and the relative expansion of normal CD19-negative BCPs, guidelines for multicolored flow cytometry data analysis and interpretation are established. The recommended approach is reliable tool for therapy response monitoring displaying the same effectiveness with the more laborious and costly molecular techniques.

Synovial sarcoma (SS) is a soft tissue tumor that occurs among a group of tumors other than rhabdomyosarcoma (RMS) in childhood and adolescence in 4 % of cases. In terms of incidence among children, SS is second only to RMS and most often occurs in young and mature patients (15–35 years), with a slight predominance in men. The localization of SS in the soft tissues of the extremities reaches 80 %; to a lesser extent, these tumors occur in the head and neck, trunk, retroperitoneal space, and joints (no more than 5 %). Cases of the appearance of SS in the mediastinum, peripheral nerves, skin and visceral organs are also described. This article presents a rare clinical case of the development of SS of the median nerve of the right shoulder in a 15-year-old patient.

The achievement of remission at the end of induction (EOI) chemotherapy in patients with acute lymphoblastic leukemia (ALL) is the key parameter of treatment effectiveness evaluation. The aim of the study – defining complete remission by multicolor flow cytometry (MFC) and bone marrow (BM) cytomorphology (CM) at the EOI chemotherapy in children with B-lineage ALL. The study was approved by the Independent Ethics Committee and the Scientific Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. The study included patients of “ALL-MB 2008” and “ALL-MB 2015” trials for whom minimal residual disease (MRD) was evaluated by MFC at the EOI simultaneously with CM BM investigation. Less than 5% blasts in BM and MRD < 1% were established as the remission achievement criteria for CM and MFC respectively. The study group included 1498 children aged from 1 to 18 years (median age was 4 years and 11 months) with B-cell precursor ALL. The overall concordance of MFC and CM was found to be 96.1% (1440 of 1498 patients). In 36 (2.4%) children with MRD ≥ 1%, M1 BM status was observed. In contrast, in 22 (1.5%) patients with M2/M3 BM status by CM, MRD value was below 1%. Treatment outcome was analyzed in 522 patients of “ALL-MB 2008” trial. Children with M2/M3 BM, as well as with MRD ≥ 1% demonstrated dramatically inferior outcome, in comparison to those who achieved remission. The presence of at least one of the mentioned criteria (M2/M3 status by CM or MRD ≥ 1% by MFC) defined a group of 23 (4.4%) patients with very low event-free survival (34.9%, standard error 11.0%) and very high cumulative incidence of relapse (56.4%, standard error 12.0%). For the evaluation of remission achievement, MFC and CM should be applied simultaneously at the EOI. High leukemic burden found by any of these methods is the clear definition of induction failure. MRD detection at the EOI should be implemented in any modern treatment protocol as an obligatory stage of treatment response monitoring and final risk group stratification. Considering the crucial importance of the MRD detection results, this study must be performed only in the reference laboratories of the study groups.

The detection of an intraocular embryonic tumor – retinoblastoma (RB) – in children and its differential diagnosis with diseases mimicking RB is an important task of imaging. Considering that the clinical and radiological patterns of RB and the diseases mimicking it may be similar, and the choice of a treatment strategy is carried out without preliminary histological examination, the primary diagnosis is of decisive importance. A comprehensive diagnostic approach for suspected RB provides a timely choice of optimal treatment tactics and improves prognosis. The article presents the most demonstrative own observations. The literature review includes the modern possibilities of non-ionizing radiation diagnostics of RB and diseases mimicking as it.

Relevance. Retinoblastoma (RB) is the most common primary intraocular tumor in children. The incidence of RB ranges from 1:14,000 to 1:20,000 newborns. To date, the survival rates of patients with RB reach almost 100 % with timely and adequate diagnosis. Among childhood oncological diseases, RB accounts for 2.3–4.5 % and 85–90 % among intraocular tumors in children. According to the volume of tumor spread, intra- and extraocular forms of the disease are distinguished. Extraocular RB is the spread of the tumor beyond the eye with invasion of the orbital tissues, as well as the possible involvement of adjacent areas, including intracranial without and with regional and/or remote metastases. The main method of treatment of children with extraocular RB is neoadjuvant chemotherapy (CT) with planning of surgical intervention and adjuvant therapy. High-dose CT (HDCT) with autologous hematopoietic stem cell transplantation (auto-HSCT), it allows to increase relapse-free survival in patients without metastatic lesions of the brain and spinal cord, but with their defeat, the prognosis of survival is extremely unfavorable, the nature of the disease is recurrent with 100 % lethality.Description of the clinical case. We report a case of bilateral RB: OD – with extraocular and intracranial spread of the tumor along the optic nerve with a lesion of the chiasm and a transition to the initial parts of the visual tracts. Secondary glaucoma. OS – with intraocular tumor growth in a 3-year-old child. After neoadjuvant chemotherapy, including intrathecal, a simultaneous two-stage operation was performed in the volume of bone-plastic (temporo-orbito-zygomatic) pterionic craniotomy on the right with prechiasmal resection of the right optic nerve and enucleation of the right eye. In the postoperative period, adjuvant chemotherapy was performed, followed by HDCT with auto-HSCT. Radiation therapy has become the final stage of treatment. Brachytherapy for OS tumor and remote radiotherapy for craniospinal region, right orbit, optic nerve stump with chiasm and pituitary pedicle were successively performed. After 14 months from the beginning of treatment and 5 months after its completion, a leptomeningeal relapse of the disease was detected.Conclusion. Rare observations of RB with damage to the visual tracts do not allow us to sufficiently study the features of the course of the tumor process, as well as to develop a single effective approach to antitumor treatment. Among the causes of mortality in patients with extraocular RB, the main one is metastasis, metastasis in the brain and spinal cord.

Contemporary therapy of acute promyelocytic leukemia (APL) is based on the use of all-trans retinoic acid, which is effective against tumor cells harboring RARa gene rearrangements (most common – t(15;17)(q24;q21)/PML::RARa). In several studies, it was suggested to use typical immunophenotypic features of APL (HLA-DR-negativity, etc) for prediction of RARa rearrangements presence. In this study, we aimed to evaluate the range of genetic aberrations that could be found in the HLA-DR-negative acute myeloid leukemia (AML). Our study was approved by the Independent Ethics Committee of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. Among studied 806 pediatric AML patients, HLA-DR-negativity was found in 253 cases. Only in 45.4% of them t(15;17)(q24;q21)/PML::RARa was found, while in remaining 54.6% normal karyotype or other genetic aberrations without RARa involvement. Frequency of the most common immunophenotypic features of APL, such as total CD117, CD33 and MPO expression with the lack of CD34, was higher in patients with t(15;17)(q24;q21)/PML::RARa, although only two thirds of APL cases were found to have all these signs. Moreover, the percentage of cells positive or negative for mentioned antigens varied significantly in APL group. Thus we can conclude, that all “typical” immunophenotypic characteristics of APL including HLA-DR-negativity, are very unspecific and cannot be used for reliable prediction of presence of t(15;17)(q24;q21)/PML::RARa.

The aim of this study was to describe the immunophenotype of leukemic cells in acute myeloid leukemia (AML) with inv(16) (p13.1q22)/CBFb-MYH11 and t(16;16)(p13.1;q22)/CBFb-MYH11 in children. This study is supported by the Independent Ethics Committee and approved by the Academic Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology. We investigated bone marrow samples from 36 pediatric patients with initially diagnosed AML with inv(16)(p13.1q22)/t(16;16)(p13.1;q22)/CBFb-MYH11. Immunophenotypic profile of leukemic cells was very heterogeneous: cells expressed antigens of early stages of differentiation (CD34, CD117, CD123) as well as markers of mature monocytes (CD11c, CD14, CD64) and neutrophils (CD65, CD15). Moreover, in 55.6% of cases lymphoid coexpressions were noticed (CD2 – the most frequent one). Furthermore, in 83.3% of cases we detected the separation of leukemic cells population into two parts: more “immature” – myeloblastic, which expressed early markers of differentiation (CD34, CD117), and more “mature” part, expressing monocytic antigens (CD11b, CD14, CD33). There was no clear separation between these parts of population. Despite the immunophenotypic similarity between monocytic part of leukemic population and normal monocytes, in 87.5% of studied cases there were same lymphoid coexpressions on these cells as on leukemic myeloblasts. Moreover, we showed that levels of CBFb-MYH11 expression in leukemic monocytes and myeloblasts were comparable. Presence of these characteristics in monocytes allows to consider them as part of leukemic cells population and take into consideration during the total immunophenotype reporting.

Relevance. The success of treatment of children with hepatoblastoma (HB) is associated primarily with the optimization of diagnostic and therapeutic strategies. The introduction of a system of therapeutic definition of a risk group developed by the International Society for the Study of Liver Tumors in Children’s Hepatic tumors International Collaboration (CHIC) in patients with HB allows for effective risk stratification. Patients of the very low-risk group have a favorable prognosis and, unlike patients of other groups, they can perform surgery at the 1st stage, and children from the very low-risk group with a “pure” fetal version of the morphological structure of the tumor can be cured without chemotherapy – only by surgical method. This article presents an analysis of a series of observations of children with HB very low-risk.Methods and patients. A retrospective analysis of the data of 138 patients who received treatment at the Research Institute of Pediatric Oncology and Hematology of N.N. Blokhin National Medical Research Centre of Oncology of the Ministry of Health of Russia from January 2006 to February 2018, all patients underwent examination in the following volume: computed tomography (CT) of the chest, ultrasound of the abdominal cavity and retroperitoneal space, CT and/or magnetic resonance imaging of the abdominal cavity with contrast enhancement. Serum levels of human chorionic gonadotropin and alpha-fetoprotein (AFP) were measured. The prevalence of tumor lesions was retrospectively evaluated using the PRETEXT system (Pre-Treatment Extent of Disease, assessment of the prevalence of the tumor process before treatment, 2017 version). Based on the data obtained, 18 (13 %) patients with hypertension were identified in the very low-risk group using the CHIC stratification system. Of 18 (100 %) patients of the very low-risk group, 8 (44.4 %) received therapy in the interval from January 2006 to October 2010 according to the treatment protocols of the SIOPEL group. The treatment included a combination of neoadjuvant chemotherapy with delayed surgery and adjuvant chemotherapy. Since November 2010, the Research Institute of Pediatric Oncology and Hematology adopted a protocol for the treatment of children with hypertension, suggesting the possibility of performing surgical treatment at the 1 st stage in patients with a localized stage of the disease with the spread of PRETEXT I/II. From December 2010 to November 2018, 10 (55.6 %) patients from the very low-risk group were operated on at the 1 st stage. A tumor biopsy was not performed before the intervention. After a histological examination, 4 (22.2 %) patients had an epithelial variant of the structure of HB that did not meet the criteria of a “pure” fetal variant. He was given adjuvant chemotherapy according to the SIOPEL protocol. And in 6 (33.3 %) patients, according to the results of a morphological study, the HB structure variant was interpreted as a “pure” fetal variant. Further therapy in this group of patients was not performed. The analysis of the results of treatment of these 6 patients without the use of chemotherapy is presented in our article.Results. The average age of patients is 3.7 (1–6) years, the median is 3.7 ± 2.0. Boys/girls – 4:2. In all cases, there was an asymptomatic course of the disease, a neoplasm was detected by chance during an ultrasound scan. All children had an elevated AFP level in the range of 95.2–695 (286.0 ± 116.8) IU/ml. Distribution according to PRETEXT I/II – 2 (33.3 %) and 4 (66.7 %) patients, respectively. Patients did not have additional PRETEXT criteria and metastases. Surgical treatment was performed by the laparoscopic method in 2 of 6 patients. Scope of operation: right-sided hemihepatectomy – 3, left-sided – 1, bisegmentectomy – 1, atypical resection – 1. Lymphatic dissection in the area of the hepatoduodenal ligament was not performed. There were no complications of treatment and repeated surgical interventions. The radicalness of the intervention in the volume of R0 was confirmed by histological examination in all patients. Morphological examination in all cases revealed a “pure” fetal version of the structure of the tumor. All patients are alive without signs of relapse at follow-up periods of 14.7 to 59.2 (32.0 ± 18.7) months.Conclusion. Using the system of therapeutic stratification into risk groups CHIC allows you to effectively distinguish patients with very low-risk groups, and for some children with a “pure” fetal version of the histological structure of the tumor, only the surgical approach can be used for treatment. At the same time, the short observation period for the patients and their small number do not allow us to draw final conclusions and dictate the need for a multicenter study. It should be noted that this cohort of patients requires careful observance of the post-therapeutic observation algorithm.