INTRODUCTION
Clear cell sarcoma of the kidney (CCSK) makes up 4 % of all primary renal malignancies in children1. Although its prognosis has significantly improved recently1-5, the relapse rate is still high and the prognosis of patients with relapses is extremely poor6. Internal tandem duplication ofBCOR (BCOR -ITD)7,8,YWHAE-NUTM2B/E fusion9,10, andBCOR -CCNB3 fusion11 have been reported in CCSK cases; however, the genetic mechanisms associated with tumor recurrence and metastasis are still poorly understood. In this study, we assessed the genetic mechanisms of CCSK recurrence and metastasis by analyzing multi-sampled tumors extracted from a single case: specimens at diagnosis, each relapse and autopsy.