Non-Wilms Renal Tumors: Twenty Years Experience in a Referral Center.

Non-Wilms Renal Tumors (NWRT) constitute less than 10% of all renal tumors diagnosed in childhood. We studied our experience in the diagnosis and management of these tumors to compare our results with the current literature. This is a retrospective observational study which includes all patients aged 0-18 years with histopathological diagnosis of NWRT treated in our center during the period 2000-2022. We identified 10 patients with diagnosis of: cystic nephroma(3), congenital mesoblastic nephroma(1), renal cell carcinoma(2), clear cell sarcoma of the kidney (2), renal Ewing's sarcoma(1) and malignant rhabdoid tumor of the kidney(1). Sixty percent (60%) were female. The median age at diagnosis was 3.25 years (IQR 1.5-10). Median age at diagnosis excluding CN was 6 years old (IQR 2.62-10.75). Molecular alterations were detected in 60% of the cases. Hematuria (40%) and palpable abdominal mass (40%) were the most frequent presenting symptoms. In total, 62.5% patients were misdiagnosed during the preoperative period as Wilms' tumor (WT), based on imaging data. A Radical nephroureterectomy was performed in all cases and staging lymphadenectomy in 70%. We recorded a major complication in one patient, who suffered a contralateral lower renal pole infarction due to section of a polar vessel during surgery. This patient had no preoperative vascular study. The recurrence-free survival rate was 90% with a median follow-up of 6.4 years (IQR 2-13.9). Radiological imaging has fundamental importance in the diagnosis of renal tumors, especially to identify children who might benefit from initial surgical treatment or the indication of biopsy for preoperative histopathological confirmation before initiating cytotoxic treatment. However, there are no pathognomonic imaging findings that clearly differentiate between WT and other renal tumors, nor among the heterogeneous group of NWRT3. In our series, 62.5% of patients were misdiagnosed as WT based on imaging features. We found different molecular alterations in 60% of our patients (Table 1). None of them predispose to the development of bilateral tumors nor correlates with predisposing syndromes of metachronous tumors. Apart from its retrospective design, this study is limited by small number of cases and a long study period. Correct differential diagnosis of NWRT is necessary for an adequate therapeutic approach. The molecular-genetic profile is an important step in the diagnosis of NWRT that allows for the use of targeted therapies in refractory patients. Detailed anatomical study by vascular mapping minimizes the risk of iatrogenic damage during tumor resection.