Materials and methods. During the period from October 2015 to February 2018, a patient cohort (n = 26) who received high-dose MTX therapy with the following nosology: osteosarcoma – 4, hemoblastosis – 11, and CNS – 11 tumors was evaluated. The average age of the patients was 7.3 years old; ratio of boys:girls – 2.25: 1. The used doses were ranged from 1 to 12 g/m², the doses schedules ranged from 4 to 36 hours; the total number of courses during the observation period was 94; the average number of courses per patient was 3. In all cases, the level of MTX in the blood serum was monitored with correction of the dose of leucovorin according to international recommendations. Estimated toxicity parameters were the following: allergic reactions, skin and mucous membrane damage, neurologic disorders, myelosuppression, hepatic transaminase and creatinine growth.

Results. Transitory toxicity was noted for 100 % of patients, of which clinically significant was in 62.7 % of cases. The development of complications that had required the use of antibacterial and blood transfusion therapy occurred after 36 courses of therapy (38.2 %), of wich in 24 cases (66.6 %) MTX was performed in combination with other antitumor agents. No cases of acute kidney injury were presented, there was no significant difference in creatinine level before and after high-dose MTX courses. The highest frequency of episodes of hepatotoxicity was noted in the group of patients diagnosed with “osteosarcoma”. After reduction the episodes of toxicity with the use of high-dose MTX, all patients continued programmed chemotherapy.

Conclusions. Against the background of an adequate accompanying therapy (infusion therapy with alkalization of urine, pharmacodynamic monitoring, correction of the leucovorin dose), it is possible to achieve satisfactory tolerability of high doses of MTX. The combination of high doses of MTX with other antitumor drugs leads to a significant increase in the toxicity. Despite of the noted complications of therapy, continuation of treatment with the use of previous doses of MTX (does not require reduction) is possible, and a decrease in the rate of MTX removal is not always a predictor of episodes of the toxicity.

In children with hematological, oncological and immunological diseases often causes complications associated with oral lesions (stomatitis, mucositis, etc.) during treatment with chemo- and radiotherapy. One way to reduce the number of such complications is individual oral hygiene and optimal selection. Aim of this study was to optimize oral hygiene based on the study of individual characteristics of patients. 18 Patients included in the study (9 with oncohematological diseases and 9 patients who did not suffer from them), who’s the main indicators of oral health were analyze in 2 stages. It was shown that patients who treated for oncohematological diseases, there is an increased risk of inflammatory changes with loss of teeth. The article presents that personal hygiene means of the oral cavity selected adequately, adherence to the oral care regime significantly improves the condition of the oral mucosa and teeth, and promotes the prevention of loss of teeth.

The risk of developing generalized bacterial infections in deeply premature infants is significantly higher than compared with the more mature newborns in terms of gestational age. In the neonatological practice, immunoglobulin preparations for intravenous administration (IVIg) are used both as a strategy for prevention and adjuvant therapy for the implementation of early and late neonatal sepsis. At the same time, the immaturity of the immune system in children with underweight and extremely low body weight is the main cause determining the ineffectiveness of IVIg medications in premature infants. Extremely actuality is the identification of factors limiting the therapeutic effectiveness of IVIg medications in premature infants, and the definition of a strategy for optimizing the effectiveness of IVIg in preterm infants with intrauterine and nosocomial infections.

The review of the literature presents the basic information on the use of intravenous immunoglobulins (IVIg) in pediatric hematology-oncology and in the context of hematopoietic stem cell transplantation in the historical perspective and at the present stage. The main requirements for IVIg are shown, which consist in the use of safe and quality solutions with a high content of immunoglobulins, which bear minimal risks for patients. The author presents the main indications, which include pathogenetic therapy of autoimmune and viral diseases (complications) and substitution therapy for the purpose of correction of secondary immunodeficiency against chemotherapy and targeted therapy.

Morphological study plays a leading role in the diagnosis, the determination of prognosis and the choice of optimal tactics of treatment of malignant neoplasms. But morphological, immunohistochemical and molecular biological diagnostic criteria for tumor pathology is inaccessible to most pathology laboratories in the regions of the Russian Federation. In one third of the cases morphological diagnosis there are errors and inaccuracies. As a result, the choice of the wrong therapeutic strategy leads to a decrease in the overall survival rates. Creation of a system of specialized reference centers for morphological diagnosis of malignant tumors will help to minimize errors. In addition, the systematization of morphological diagnoses within the framework of the national children's population cancer register will allow carrying out oncoepidemiological studies among the children of the Russian Federation. National medical research center of pediatric Hematology, Oncology and immunology named after Dmitry Rogachev is now effectively plays the role of such a centre. During the period 2012–2016 72.361 histological studies, 103.029 immunohistochemical studies, 6507 histochemical studies, 618 studies using in situ hybridization methods were conducted. Material for reference diagnostics was received from 63 territories of the Russian Federation. The increased load on the pathology laboratory staff causes the formation of a system of similar centers of morphological diagnostics with justification of the status, expansion of staff, legal and financial support.

Cytomegalovirus (CMV) infection is one of the most an issue of common complications among patients receiving polychemotherapy. However, the question of the influence of CMV infection remains under-explored outside the context of allogeneic transplantation of hematopoietic stem cells. The article presents a rare clinical case – achievement of complete clinical and hematological remission of refractory neuraleukemia against CMV infection in a patient with acute myeloblastic leukemia, followed by rejection of hematopoietic transplants against the background of activation of the TcRα/β-clone of lymphocytes and CMV viremia.

Improving the methods of diagnostic and treating malignant neoplasms in children remain a major challenge of modern pediatrics. Despite of the achievements made in the treatment of the monolateral nephroblastoma, the ambilateral kidney dysfunction by the Wilms tumor induses a number of difficulties among the pediatric oncologist at the diagnostic phase, particularly in the setting of the strategy and tactics used in the antitumor therapy. This article represents clinical case of decreasing Bilateral nephroblastoma in children of 5 years.

The article presents a case of development of bone tissue damage as a manifestation of toxicity against the background of differentiation therapy of 13-cis-Retinoic acid in a patient with neuroblastoma (NB) of a high-risk group. This clinical example is of interest as a model of a differential diagnosis of metastatic osseous lesion in patients with disseminated NB and a rare variant of bone toxicity during specific therapy.

This work is focused on the analysis of problems associated with the state of the gastrointestinal tract (GI tract) in patients who underwent a malignant neoplasm in childhood. The main diseases and pathological conditions that can develop in this population are considered. The risks of development of pathological changes on the part of the GI tract, their treatment and prevention are described. Separately, the question of organ-specific liver damage, including hepatitis B and C examined.

In 2017 the organization of the children’s hematology service celebrated the 50th jubilee in St. Petersburg. The first specialized children’s hematology department in Leningrad (now St. Petersburg) was opened in 1967. Over the years, a strong network of institutions that allowed to provide highly qualified assistance to all children in need with hematological diseases has been formed in the city with the population greater than 5 million: the number of divisions reached seven and its curative capacity is more than 180 beds. The article describes the main phase of the development of the hematological service in St. Petersburg.