Metanephric tumors in children and adolescents: clinical, morphological and molecular genetic characteristics
Authors: Smirnova L. A. , Mitrofanova A. M. , Teleshova M. V. , Merkulov N. N. , Konovalov D. M. , Akhaladze D. G. , Druy A. E. , Raykina Е. V. , Shamanskaya T. V. , Grachev N. S. , Kachanov D. Yu. 
Published: October 2024

Metanephric tumors (MTs) are a group of rare childhood kidney tumors consisting of epithelial and/or stromal cellular elements and characterized by a variety of histopathological features. MTs include metanephric adenoma (MA), metanephric adenofibroma (MAF), and metanephric stromal tumor (MST). This study aimed to retrospectively analyse clinical and molecular genetic characteristics of MTs, verified at the Pathology Department of the Dmitry Rogachev NMRCPHOI of Ministry of Healthcare of the Russian Federation. The study was approved by the Independent Ethics Committee and the Scientific Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of Ministry of Healthcare of the Russian Federation. We performed a retrospective analysis of data on patients with MTs histologically confirmed between February 2015 and February 2024 (109 months). During this period, a total of 26 cases (patients aged 0–18 years) of histologically confirmed MA, MAF, and MST had been documented at the Pathology Department of the D. Rogachev Center. Out of these 26 cases, 16 patients with known clinical data were included in our analysis. The median age at diagnosis was 3.5 years (range: 0.4–15.2 years). The boys:girls ratio was 1:1. The analysis of primary complaints showed that the majority of patients (n = 8; 50%) were asymptomatic and their kidney masses were detected by chance. The rest of the patients presented with pain syndrome (n = 3; 19%), gross hematuria (n = 2; 13%), intoxication syndrome (n = 1; 6%), polycythemia (n = 1; 6%), an increased abdominal circumference (n = 1; 6%). Primary surgery was performed in 6 (37%) patients: partial nephrectomy (n = 4), total nephrectomy (n = 1), and a core needle biopsy of the mass followed by partial nephrectomy (n = 1). Ten patients (63%) underwent preoperative multiagent chemotherapy. The analysis of the extent of surgical treatment of all patients included in the analysis (n = 16) showed that total nephrectomy was performed in 9 cases, and partial nephrectomy – in 7 cases. R0 resection was achieved in 15 cases, R1 resection – in 1 case. The distribution by histological variants was as follows: MA – 10 (63%) patients, MST – 3 (19%) patients, MAF – 1 (6%) patient, MA in combination with clear cell papillary renal cell carcinoma – 1 (6%) patient, MAF in combination with papillary renal cell carcinoma – 1 (6%) patient. Sixteen patients underwent molecular genetic testing: a somatic V600E mutation in the BRAF gene was detected in 10/16 (62.5%) patients. Currently, all patients are alive, and no relapses of the disease have been observed. MTs are a group of rare kidney tumors in children, characterized by a variety of histological patterns, which creates difficulties in differential diagnosis with other kidney tumors, such as renal cell carcinoma and nephroblastoma. Molecular genetic testing aimed at identifying mutations in the BRAF gene can help in establishing the correct morphological diagnosis.