The strategy of avoiding RT for LR and IR patients that responded completely to ABVD chemotherapy achieved very good results. For the HR group, the combination of 6 cycles of ABVD and Low-dose involved field radiotherapy was efficacious with similar good results. Nearly half of the patients could be cured without RT.

Progressive nodular histiocytosis is a rare variant of non‐Langerhans cell histiocytosis that affects the skin and mucous membranes and displays a progressive clinical course and poor response to treatment. We describe a case of severe progressive nodular histiocytosis harboring a KRAS p.G12S mutation in a 9‐year‐old boy, refractory to chemotherapy, who was successfully treated with the MEK inhibitor cobimetinib. This is the first report of the use of MEK inhibition for this histiocytosis subtype in a pediatric patient.

Spinal cord compression (SCC) is an unusual manifestation of leukemias and lymphomas in children and defines an oncological emergency frequently unsuspected, being a cause of severe sequelae. Our aim was to analyze the characteristics of patients who presented signs or symptoms of spinal cord compression in early phases of malignant hematopoietic diseases. From November-1988 to July-2022, 3878 patients with leukemia and lymphoma were diagnosed. Of them, 36 children (0.92%) presented spinal cord compression signs/symptoms in early phases of their diagnosis: Acute Lymphoblastic Leukemia (n=18), Acute Myeloblastic Leukemia and Myeloid Sarcoma (n=7), Non-Hodgkin Lymphomas (n=9) and Hodgkin Lymphoma (n=2). Clinical characteristics, images and hematological findings, treatment strategies, results and sequelae were analyzed. Sex distribution was 3.5/1 (M/F) and the media age at diagnosis was 10 (range: 4.9-16.9) years. The most common symptoms were back pain (34/36), functional impotence (27/36) and sphincter compromise (10/36). The media time from symptom onset to diagnosis was 47,5 (range: 0-300) days. Magnetic resonance imaging was performed on 33 (92%) patients and showed epidural mass (n=16) or vertebral collapse (n=17) in all of them. Two patients received initial radiotherapy and 11 decompressive surgeries for the management of the urgency spinal cord compression. Bone marrow aspiration was the diagnostic procedure in 69% of cases. All patients received chemotherapy and 94% achieved complete remission. Severe sequelae were observed in 10 patients (paraplegia with neurogenic bladder and kyphoscoliosis). Leukemia and lymphoma should be considered as a differential diagnosis when spinal cord compression is suspected, and magnetic resonance imaging is the mandatory study to confirm this diagnosis as a matter of urgency. Bone marrow involvement was evident due to hematological alterations in 95% of cases allowing to guide the diagnosis and initiate treatment early to reduce sequelae.

Introduction: Acute Megakaryoblastic Leukemia (AMKL) is an unusual AML subtype in childhood, being the most frequent AML in Down syndrome (DS) patients. AMKL corresponds to 19.3% of AML in our Hospital and some special characteristics have been observed. Objective: To analyze characteristics of AMKL and to compare patients with or without DS. Patients and Methods:From January-1990 to June-2014 AMKL was diagnosed in 77 cases: 57 in non-DS and 20 in DS children. Fivecases were secondary leukemias and 3 cases had been previouslytreated with chemotherapy due to wrong diagnosis. One patient was on induction at the time of analysis. These 9 cases were not evaluable for follow-up. Forty-eight non-DS and 20 DS caseswere evaluable. Megakayocyte lineage commitment was confirmed in all cases by fluorescence microscopy. MPO was analyzedboth by flow cytometry and cytochemistry. G-banding and RT-PCR were performed according to standard techniques. Four successive BFM-based protocols were administeredwith schedule modification for DS patients. Results: Mean age was:2 (range: 2 mo-13 y) years of age and mean WBC count was: 27,500 (range: 1,600-250,000)/mm3. No differences were observed in age or hematological findings at diagnosis. Extramedullar compromise was detected in 10 (17.5%) of non-SD cases. Immunophenotype defined ambiguous lineage leukemia in 3 (5.0%) of the non-DS cases, with compromise of T-lineage. Interestingly, in 4 cases the megakaryoblasts also co-expressed MPO.Cytogenetic findings showed hyperdiploidy (n=7), t(1;22)(p13;q23) (n=3), t(16;21)/FUS-ERG (n=2), abnormalities in chromosome 7 (n=5) and complex karyotype (n=9). Complete remission (CR) was achieved in 51 (33 non-DS and 18 DS) (75.0%) of 68 evaluable cases;null-responses observed in7(only non-DS, 10.3%). Early deaths occurred in 10 (14.7%) during induction phase, 2 of them before treatment onset. From the 51 patients who achieved CR, 16 (14 non-DS and 2 DS) presented relapses(p: 0.04) and 9 (6 in non-DS and 3 in DS) died in CR. EFS-probability for the total population was 34 (6)%, for non-DS 21 (6)% and for DS 63 (11)%(p-value: 0.0026). LFS-probability was 45 (7)% for the total population, for non-DS 29 (8)% and for DS 70 (11)% (p-value: 0.0117). Median follow-up: 148 (range: 2-194) months. Conclusions: 1- Extramedullar compromise and T/myeloid mixed lineage or co-expression of MPO were observed only in non-DS AMKL, in 17.5% and 12.0% respectively. 2- Null-response was observed only in non-SD patients. 3- The most frequent event of non-DS was relapse, and toxic deaths in DS. 4- The significantly better outcome of patients with DS was confirmed in our setting. Disclosures No relevant conflicts of interest to declare.

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