[Clinicopathological characteristics of anaplastic sarcoma of the kidney in children].

Objective: To study the clinical and pathological features of anaplastic sarcoma of the kidney(ASK) in children, and to explore its molecular profiles and differential diagnosis. Methods: Five cases of pediatric ASK diagnosed at Beijing Children's Hospital, Beijing, China from January 2018 to June 2025 were collected. The clinical, histological, and immunohistochemical features were analyzed. Three cases were subjected to TP53 detection using fluorescent in-situ hybridization (FISH), and DICER1 and TP53 detection using PCR amplification and Sanger sequencing. Results: There were 3 males and 2 females. The patients' ages ranged from 1.6 years to 17.7 yeas, with an age of 8.2 (3.8, 12.7). A renal mass was accidentally found in 1 case, and abdominal pain with hematuria was present in 4 cases. Four cases were presented as a unilateral tumor, while one as bilateral tumors. The radiographic features of ASK were cystic and solid masses. The tumors were staged as stage Ⅰ, Ⅴ, Ⅳ, Ⅱ and Ⅱ, respectively. Histologically, all tumors showd both cystic and solid areas, spindle cell components with anaplastic changes and frequent atypical mitotic figures, arranged in a fascicular pattern. Chondroid differentiation and rhabdomyoblasts features were present. Multiloculated cysts showed cystic nephroma-like foci, and subepithelial primitive cells with cambium-like layer appearance. Immunohistochemistry showed that desmin was positive in 3 of the 5 cases, and myogenin and MyoD1 were positive in 2 of the 5 cases. p53 was overexpressed(mutated type) in 2 cases, loss of expression(null type) in 1 case and wild type in 1 case. Ki-67 positive rates were 30%-90%. Three cases with sequencing information harbored DICER-1 mutations(somatic and truncating mutations) and loss of TP53 gene. One patient with bilateral tumors died during follow-up. Another patient had distant metastasis, while the others had no recurrence or metastasis. Conclusions: ASK in children is a rare DICER1-related tumor, with distinct histologic features and biological behavior. The differential diagnosis includes anaplastic Wilms tumor, clear cell sarcoma of the kidney, etc. Integration of clinical manifestations, histology, immunohistochemistry, and molecular studies may be required to render correct diagnosis.