Clinical, morphological, and genetic characteristics of children with clear cell sarcoma of the kidney

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Abstract
Introduction . Clear cell sarcoma of the kidney (CCSK) is a rare primary renal tumor in children. It is characterized by an aggressive course, rapid tumor growth, and a high propensity for metastasis. Clinical interest in CCSK stems not only from its aggressiveness as a distinct entity but also from the diagnostic challenges in differentiating it from other pediatric renal neoplasms. Standardization of diagnosis and optimization of therapy require the identification of molecular markers to improve differential diagnosis with other rare renal tumors. A comprehensive approach – from early detection by pediatricians to precise molecular genetic testing – is essential to improve prognosis. The purpose of the study – to evaluate the clinical, morphological, and molecular genetic features of CCSK. Materials and methods . We conducted a retrospective single-center study of children with CCSK who received treatment at the Research Institute of Pediatric Oncology and Hematology named after Academician L.A. Durnov, N.N. Blokhin National Medical Research Center of Oncology, Ministry of Health of Russia, between September 2009 and December 2023. Results . Prognostic factors assessed included sex, age at diagnosis, primary tumor volume, and molecular genetic characteristics. The cohort was predominantly male (15/22, 68 %) compared with female (7/22, 32 %). Median age at diagnosis was 29 (17–44) months, and median primary tumor volume was 543 (368–748) cm3 . All tumors were unilateral (right-sided – 45 %, left-sided – 55 %). Localized disease was present in 21 (95.5 %) patients and metastatic disease in 1 (4.5 %); no pulmonary metastases were detected at diagnosis. No significant sex differences were observed in age or tumor volume (p > 0.05). At a median follow-up of 4.1 years, 6 events (27.3 %) and 2 deaths (9.1 %) occurred. Event-free survival (EFS) was 100 % at 1 year, 79.6 % (95 % confidence interval 63.4–99.9) at 3 years, and 72.4 % (95 % confidence interval 53.9–97.1 %) at 5 years. Overall survival (OS) was 100 %, 88.4 %, and 88.4 % (95 % confidence interval 74.3–100 %), respectively. Median EFS and OS were not reached; median time to event was 2.5 (1.7–5.6) years. Age < 2.7 years (cutoff – 32 months) showed a trend toward inferior EFS (p = 0.096, log-rank). No differences in EFS were found according to sex (p = 0.954), tumor volume (p = 0.446), or treatment protocol (Umbrella SIOP-RTSG 2016 (n = 12) vs. other regimens (SIOP-93-01, SIOP-2001; n = 10) (p = 0.6). Molecular genetic testing was performed in 7 patients (32 %); BCOR internal tandem duplication was identified in all 7 (100 %). Conclusions . Age younger than 2.7 years may represent a potentially unfavorable prognostic factor in CCSK. The median time to first event of 2.5 years indicates that most relapses occur in the medium-term period after therapy completion.

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