Objective:To investigate a new method for rapid detection of the MYOD1 L122R mutation and to analyze the clinical and pathological characteristics of mutation-positive rhabdomyosarcoma.Methods:A MYOD1 mutation detection kit was developed using allele-specific Taqman fluorescence probe technology. A total of 80 rhabdomyosarcoma samples diagnosed at Beijing Children′s Hospital, Capital Medical University from June 2022 to June 2023 were collected for testing. The detection sensitivity, specificity, and consistency rate of the kit were compared with those of the gold standard Sanger sequencing. The demographic, histopathological, and molecular genetic characteristics of patients with MYOD1 mutations were analyzed.Results:Among the 80 rhabdomyosarcoma cases, there were 46 males and 34 females, with an age of onset ranging from 0 to 16 years [mean (6.0±4.4) years], including 32 embryonal rhabdomyosarcoma, 18 alveolar rhabdomyosarcoma, and 30 spindle cell/sclerosing rhabdomyosarcoma. The new kit screened a total of 11 mutations, of which 10 were spindle cell/sclerosing rhabdomyosarcoma and one was embryonal rhabdomyosarcoma. Patients with MYOD1 mutations were typically older (four cases over 10 years old) but could also occur in young children (the youngest being 3-year and 2-month-old). The primary sites were the head and neck region in eight cases, limbs in two cases, and pelvic cavity in one case. Among the six patients with available staging information at initial diagnosis, one was classified as stage 2 and five were stage 3, all of which were intermediate risk. Among the 11 mutation patients, six had recurrence and metastasis, with three deaths; the remaining patients had not shown tumor progression until last follow-up. Compared with the wild type group, the expression level of MYOD1 in mutation patients increased significantly ( χ2=10.66, P=0.01), while the event-free survival rate ( χ2=9.925, P<0.01) and overall survival ( χ2=4.53, P=0.03) rate decreased. Compared with Sanger sequencing, the kit achieved 100% sensitivity and specificity. The kit had a minimum mutation content detection limit of 2% and the reaction could be finished within 2 hours. Additionally, this kit might also be used to detect the expression of MYOD1, thereby aiding the diagnosis of rhabdomyosarcoma. Conclusions:The study has established a new method for accurate and rapid detection of MYOD1 mutation in rhabdomyosarcoma, particularly suitable for the formalin-fixed and paraffin-embedded samples in clinical settings. MYOD1 mutations more likely occur in spindle cell/sclerosing rhabdomyosarcoma of the head and neck region in children. Patients with MYOD1 mutations have an extremely poor prognosis, which is independent of clinical staging and grading. MYOD1 mutation detection in rhabdomyosarcoma has significant value for auxiliary diagnosis and prognostic assessment.

Objective:To investigate the clinicopathological and molecular genetic characteristics of pediatric tumors with DICER1 mutations.Methods:A total of 90 patients diagnosed with various types of pediatric tumors at Beijing Children′s Hospital, Capital Medical University, Beijing, China from July 2023 to September 2025 were included in this study. PCR amplification and Sanger sequencing were performed to detect the coding-region mutations of the DICER1 gene. The clinical, histopathological, and molecular genetic features of the cases with DICER1 mutation were then analyzed.Results:Among the 90 patients, 39 were male and 51 were female, with an age of onset ranging from 1 month to 17 years [median 7.13 (2.77, 10.37) years]. DICER1 mutations were detected in 37 patients (37/90, 41.1%). Among them, 9 cases harbored one mutation [6 pleuropulmonary blastomas (PPBs), 2 sex cord stromal tumors (SCSTs), and 1 cystic nephroma (CN)], 27 cases carried two mutations [10 PPBs, 3 anaplastic sarcomas of the kidney (ASKs), 3 SCSTs, 3 thyroid adenoma, 2 nodular thyroid goiters, 2 thyroid follicular lesions, 2 CN, 1 embryonal rhabdomyosarcoma, and 1 case with multiple primary tumors], and 1 case exhibited three mutations (bilateral ASKs). Despite variations in the site of origin, DICER1-mutant tumors shared several morphological features. Grossly, they presented as multilocular cystic, cystic-solid to solid masses. Microscopically, they exhibited a subepithelial layer of mesenchymal cells, with focal rhabdomyoblastic/chondroid/chondrosarcomatous differentiation, as well as cellular anaplasia. Germline testing using peripheral blood in the 31 patients with DICER1 mutation confirmed germline origin in 61.3% (19/31) of them. Parental analysis ( n=12) demonstrated genetic inheritance in 8 cases, predominantly from families with tumor history. Germline variants scattered throughout DICER1 and consisted of loss-of-function mutations (nonsense, frameshift, and splice-site). Somatic mutations showed distinct clustering in exons 24 and 25 hotspots (codons 1705, 1709, 1809, 1810 and 1813), primarily missense variants. Notably, one multiple primary tumor case harbored a somatic mosaic p.E1705K mutation. Conclusions:DICER1 mutations are frequently detected in pediatric PPB, CN, SCST, ASK, nodular thyroid goiter, thyroid adenoma, and genitourinary rhabdomyosarcoma, which often represent as the index case of DICER1 syndrome. Performing DICER1 mutation testing in these patients not only facilitates tumor diagnosis and secondary cancer surveillance, but also enables the comprehensive genetic risk assessment and management for patient′s family members.

Pediatric urological non-Hodgkin lymphoma is relatively rare.When a single renal or ureteral tumor with multiple lymph node or bone metastases is present, it is very easy to be misdiagnosed as urinary tumor with metastasis, resulting in unnecessary radical nephrectomy. This paper reports two cases of non-Hodgkin lymphoma presenting with single urinary nodules. Case 1 was diagnosed with a 4.5cm tumor in the right kidney due to fever and fatigue. CT and PET-CT showed multiple bone destruction and lymph node metastasis. Renal biopsy was performed and ALK-positive anaplastic large cell lymphoma was diagnosed. Chemotherapy was effective for 6 months. Case 2 was diagnosed with left hydronephrosis due to intermittent low back pain for 2 weeks. Ultrasound examination revealed ureteral dilation with left hydronephrosis and low echo occupying of the lower ureter. The patient had sudden blurred vision before surgery. MRI examination revealed space occupying in the right optic nerve frame, and PET-CT found multiple bone, lymph nodes and nerve invasion. A lymph node biopsy was performed and Burkitt lymphoma was diagnosed. After 6 months of chemotherapy and radiotherapy, the tumor shrank significantly.

Objective:To investigate the clinicopathological and molecular genetic characteristics of pediatric tumors with DICER1 mutations.Methods:A total of 90 patients diagnosed with various types of pediatric tumors at Beijing Children′s Hospital, Capital Medical University, Beijing, China from July 2023 to September 2025 were included in this study. PCR amplification and Sanger sequencing were performed to detect the coding-region mutations of the DICER1 gene. The clinical, histopathological, and molecular genetic features of the cases with DICER1 mutation were then analyzed.Results:Among the 90 patients, 39 were male and 51 were female, with an age of onset ranging from 1 month to 17 years [median 7.13 (2.77, 10.37) years]. DICER1 mutations were detected in 37 patients (37/90, 41.1%). Among them, 9 cases harbored one mutation [6 pleuropulmonary blastomas (PPBs), 2 sex cord stromal tumors (SCSTs), and 1 cystic nephroma (CN)], 27 cases carried two mutations [10 PPBs, 3 anaplastic sarcomas of the kidney (ASKs), 3 SCSTs, 3 thyroid adenoma, 2 nodular thyroid goiters, 2 thyroid follicular lesions, 2 CN, 1 embryonal rhabdomyosarcoma, and 1 case with multiple primary tumors], and 1 case exhibited three mutations (bilateral ASKs). Despite variations in the site of origin, DICER1-mutant tumors shared several morphological features. Grossly, they presented as multilocular cystic, cystic-solid to solid masses. Microscopically, they exhibited a subepithelial layer of mesenchymal cells, with focal rhabdomyoblastic/chondroid/chondrosarcomatous differentiation, as well as cellular anaplasia. Germline testing using peripheral blood in the 31 patients with DICER1 mutation confirmed germline origin in 61.3% (19/31) of them. Parental analysis ( n=12) demonstrated genetic inheritance in 8 cases, predominantly from families with tumor history. Germline variants scattered throughout DICER1 and consisted of loss-of-function mutations (nonsense, frameshift, and splice-site). Somatic mutations showed distinct clustering in exons 24 and 25 hotspots (codons 1705, 1709, 1809, 1810 and 1813), primarily missense variants. Notably, one multiple primary tumor case harbored a somatic mosaic p.E1705K mutation. Conclusions:DICER1 mutations are frequently detected in pediatric PPB, CN, SCST, ASK, nodular thyroid goiter, thyroid adenoma, and genitourinary rhabdomyosarcoma, which often represent as the index case of DICER1 syndrome. Performing DICER1 mutation testing in these patients not only facilitates tumor diagnosis and secondary cancer surveillance, but also enables the comprehensive genetic risk assessment and management for patient′s family members.

Pediatric urological non-Hodgkin lymphoma is relatively rare.When a single renal or ureteral tumor with multiple lymph node or bone metastases is present, it is very easy to be misdiagnosed as urinary tumor with metastasis, resulting in unnecessary radical nephrectomy. This paper reports two cases of non-Hodgkin lymphoma presenting with single urinary nodules. Case 1 was diagnosed with a 4.5cm tumor in the right kidney due to fever and fatigue. CT and PET-CT showed multiple bone destruction and lymph node metastasis. Renal biopsy was performed and ALK-positive anaplastic large cell lymphoma was diagnosed. Chemotherapy was effective for 6 months. Case 2 was diagnosed with left hydronephrosis due to intermittent low back pain for 2 weeks. Ultrasound examination revealed ureteral dilation with left hydronephrosis and low echo occupying of the lower ureter. The patient had sudden blurred vision before surgery. MRI examination revealed space occupying in the right optic nerve frame, and PET-CT found multiple bone, lymph nodes and nerve invasion. A lymph node biopsy was performed and Burkitt lymphoma was diagnosed. After 6 months of chemotherapy and radiotherapy, the tumor shrank significantly.

Objective:To investigate a new method for rapid detection of the MYOD1 L122R mutation and to analyze the clinical and pathological characteristics of mutation-positive rhabdomyosarcoma.Methods:A MYOD1 mutation detection kit was developed using allele-specific Taqman fluorescence probe technology. A total of 80 rhabdomyosarcoma samples diagnosed at Beijing Children′s Hospital, Capital Medical University from June 2022 to June 2023 were collected for testing. The detection sensitivity, specificity, and consistency rate of the kit were compared with those of the gold standard Sanger sequencing. The demographic, histopathological, and molecular genetic characteristics of patients with MYOD1 mutations were analyzed.Results:Among the 80 rhabdomyosarcoma cases, there were 46 males and 34 females, with an age of onset ranging from 0 to 16 years [mean (6.0±4.4) years], including 32 embryonal rhabdomyosarcoma, 18 alveolar rhabdomyosarcoma, and 30 spindle cell/sclerosing rhabdomyosarcoma. The new kit screened a total of 11 mutations, of which 10 were spindle cell/sclerosing rhabdomyosarcoma and one was embryonal rhabdomyosarcoma. Patients with MYOD1 mutations were typically older (four cases over 10 years old) but could also occur in young children (the youngest being 3-year and 2-month-old). The primary sites were the head and neck region in eight cases, limbs in two cases, and pelvic cavity in one case. Among the six patients with available staging information at initial diagnosis, one was classified as stage 2 and five were stage 3, all of which were intermediate risk. Among the 11 mutation patients, six had recurrence and metastasis, with three deaths; the remaining patients had not shown tumor progression until last follow-up. Compared with the wild type group, the expression level of MYOD1 in mutation patients increased significantly ( χ2=10.66, P=0.01), while the event-free survival rate ( χ2=9.925, P<0.01) and overall survival ( χ2=4.53, P=0.03) rate decreased. Compared with Sanger sequencing, the kit achieved 100% sensitivity and specificity. The kit had a minimum mutation content detection limit of 2% and the reaction could be finished within 2 hours. Additionally, this kit might also be used to detect the expression of MYOD1, thereby aiding the diagnosis of rhabdomyosarcoma. Conclusions:The study has established a new method for accurate and rapid detection of MYOD1 mutation in rhabdomyosarcoma, particularly suitable for the formalin-fixed and paraffin-embedded samples in clinical settings. MYOD1 mutations more likely occur in spindle cell/sclerosing rhabdomyosarcoma of the head and neck region in children. Patients with MYOD1 mutations have an extremely poor prognosis, which is independent of clinical staging and grading. MYOD1 mutation detection in rhabdomyosarcoma has significant value for auxiliary diagnosis and prognostic assessment.

Purpose To study the clinical and pathological features of angiomatoid fibrous histocytoma(AFH)and to ex-plore its diagnosis,differential diagnosis and prognosis.Meth-ods The clinicopathological and follow-up data were analyzed in 14 cases of AFH,and the literatures were reviewed.Results There were 11 males and 3 females.The age ranged from 11 months to 12 years and 11 months,with average 5.9 years.3 cases were located in limbs,and 5 cases in trunk,5 cases in head and neck region,and 1 of intracranial tumor.Histological-ly,14 cases were composed of fibrous capsules and lymphocyte sheaths,and cell nucleus were vacuolar,forming fascicles with focal whirling and synteny.Intralesional pseudoangiomatous spaces were noted in 9 cases.Calcification was found in 2 ca-ses.2 cases showed high mitotic acticity(11/10 HPF).Scle-rosing and/or myxoid stroma was seen in 3 cases.Tumors were immunopositive for desmin(10/14),EMA(12/14),CD99(12/14),SMA(9/12),ALK(7/8),and the average of Ki67 index was 16％.7 cases harbored EWSR1 rearrangenent(part-ner gene not identified),2 cases had EWSR1-ATF1 fusion and 2 EWSR1-CREB1 fusion.Clinical follow-up information was a-vailable for 14 cases(average 46 months).All the 14 cases were alive without recurrence and metastasis.Conclusion AFH is a borderline or low-grade malignant tumor,often demon-strates indolent behavior in children,but rarely recurs and me-tastasizes.The diagnosis and differential diagnosis require a comprehensive analysis of clinical features,histopathologic changes,immunohistochemical finding and EWSR1 or FUS gene detection results.

Objective:To investigate the relationship between 1p/16q loss of heterozygosity (LOH) and 1p gain in Wilms tumor and their clinicopathologic characteristics and prognosis.Methods:A total of 175 Wilms tumor samples received from the Department of Pathology, Beijing Children′s Hospital from September 2019 to August 2022 were retrospectively analyzed. The histopathologic type and presence of lymph node involvement were evaluated by two pathologists. The clinical data including patients′gender, age, tumor location, preoperative chemotherapy, and tumor stage were summarized. Fluorescence in situ hybridization (FISH) was done to detect 1p/16q LOH and 1p gain and their correlation with the clinicopathological features and prognosis were analyzed.Results:Among the 175 samples, 86 cases (49.1%) were male and 89 (50.9%) were female. The mean age was (3.5±2.9) years, and the median age was 2.6 years. There were 26 (14.9%) cases with 1p LOH, 28 (16.0%) cases with 16q LOH, 10 (5.7%) cases of LOH at both 1p and 16q, and 53 (30.3%) cases with 1q gain. 1q gain was significantly associated with 1p LOH ( P<0.01) and 16q LOH ( P<0.01). There were significant differences ( P<0.01) between 1q gain, 1p LOH and 16q LOH among different age groups. The rate of 16q LOH in the high-risk histopathological subtype (50.0%) was significantly higher than that in the intermediate-risk subtype (13.6%, P<0.05). The frequency of 1q gain, 1p LOH, and 16q LOH in children with advanced clinical stages (Ⅲ and Ⅳ) was significantly higher than that in children with early clinical stages (Ⅰ and Ⅱ). 1q gain, 1p LOH, and 16q LOH showed no significant correlation with gender, unilateral or bilateral disease, chemotherapy, or lymph node metastasis. The progression-free survival (PFS) time for patients with 1q gain and 1p LOH was significantly shorter than those without these aberrations ( P<0.05). Additionally, the PFS time of patients with 16q LOH was slightly shorter than those with normal 16q, although the difference was not statistically significant. Patients with stage Ⅲ to Ⅳ disease exhibiting 1q gain or 1p LOH had a significantly higher relative risk of recurrence, metastasis, and mortality. Conclusions:1p/16q LOH and 1q gain are associated with age, high-risk histological type, and clinical stage in Wilms tumor. 1q gain and 1p LOH are significantly correlated with the prognosis of Wilms tumor.

Objective:To investigate the clinicopathological features, immunophenotype and molecular genetic characteristics of congenital spindle cell/sclerosing rhabdomyosarcoma.Methods:Sixteen cases (including 10 consultation cases) of congenital spindle cell/sclerosing rhabdomyosarcoma diagnosed at the Beijing Children′s Hospital, Capital Medical University, Beijing China, from April 2017 to January 2022 were collected. These cases were evaluated for clinical profiles, histomorphological features, immunophenotype and molecular characteristics.Results:Among the 16 patients, 9 were male and 7 were female. Five cases were present during maternal pregnancy and 11 cases were found immediately after birth. The tumors were located in the chest wall, low back, retroperitoneum, extremities or perineum. The tumors consisted of fasciculated spindle-shaped cells with localized mesenchymal sclerosis and vitreous metaplasia. Immunohistochemistry showed that the tumor cells expressed Desmin, Myogenin, MyoD1, SMA, CD56 and ALK to varying degrees, but not other markers such as CD34, CD99, pan-TRK, S-100 and BCOR. FISH analyses with NCOA2 (8q13) and VGLL2 (6q22) gene breakage probes revealed a breakage translocation in chromosome NCOA2 (8q13) in 4 cases (4/11). In the 6 cases subject to sequencing, a mutation at the p.L122R locus of MYOD1 gene was detected in 1 case (1/6). Two cases were examined by electron microscopy, which showed bundle-arranged myofilaments with some primitive myofilament formation. Five cases were resected with simple surgery, 2 cases were biopsied and followed up with observation only, and 9 cases were treated with surgery and adjuvant chemotherapy. Follow-up was available in 12 cases. At the end of the follow-up, 2 of the 12 patients developed local recurrences and 2 patients survived with disease.Conclusions:Congenital spindle cell/sclerosing rhabdomyosarcoma is a rare subtype of congenital rhabdomyosarcoma. It more commonly occurs in the chest, back and lower limbs of infants than other sites. NCOA2/VGLL2 gene fusion seems to be the most common genetic change. Its prognosis is better than other subtypes of rhabdomyosarcoma and those in adolescents and adults with the same subtype. Analysis and summary of its clinicopathological features can help differentiate it from other soft tissue tumors in infants and children and provide the information for appropriate treatments.

Objective To investigate the CT and MRI features of intraosseous myofibroma/myofibromatosis in pediatric patients.Methods The retrospective analysis involved the examination of clinical data and imaging findings from 15 children who were diagnosed with myofibroma/myofibromatosis of bone invasion through pathological means.Subsequently,the imaging characteristics were summarized.Results CT examinations were conducted on a total of 15 patients,with 2 of them also received enhanced scans.Additionally,MRI examinations were conducted on 5 patients,with 3 of them also underwent enhanced scans.Eleven patients were diagnosed with solitary type myofibroma,with 7 cases localized in the skull and the remaining lesions observed in the maxillofacial bone.Three patients exhibited the multicentric type without any involvement of visceral organs,while one patient presented with the multicentric type accompanied by visceral involvement.The lesions exhibited a uniform soft-tissue density on plain CT scan,predominantly located between the inner and outer layers of the bone.Additionally,they displayed swelling changes and osteolytic bone destruction,with some lesions showed residual bone shell.On MRI,the lesions exhibited a uniform signal,demonstrated an isointense or slightly hypointense signal on T1WI and an isointense or slightly hyperintense signal on T2WI.The lesions displayed significantly heterogeneous enhancement on CT and MRI.Conclusion The imaging manifestations of intraosseous myofibroma/myofibromatosis in pediatric patients exhibit certain characteristics,and the residual bone shell in the lesion is helpful for diagnosis,however,distinguishing it from Langerhans cell histiocytosis of the bone remains challenging,necessitating the reliance on pathological diagnosis.