The Japan Wilms Tumor Study group (JWiTS) was founded in 1996 to improve outcomes for children with renal tumor in Japan, and a nationwide multicenter cooperative study was initiated thereafter. JWiTS-1 (1996-2005) was analyzed, and JWiTS-2 (2005-2014) is now under analysis; the following problems have been identified and used to decide future study protocol: (i) there has been a decline in survival rate for patients with rhabdoid tumor of the kidney (RTK) and new treatment strategies are required; (ii) the survival rate for bilateral Wilms tumors (BWT) has improved, but results for renal preservation are unsatisfactory; (iii) the prognosis of stage IV favorable nephroblastoma is very good, suggesting that the current protocols provide overtreatment, particularly for patients with lung metastasis; and (iv) no effective biological risk factors exist for predicting the outcome of Wilms tumor, and a study of the genetic changes of these tumors is necessary to determine biological markers for use in risk classification. To solve these issues, the development of a new risk classification of pediatric renal tumors is required. In addition, different study protocols should be developed according to the risk-based classification of the patients. Further, a new study protocol for BWT began in 2015, and new study protocols are being prepared for RTK, and for Wilms tumor with lung metastasis. In addition, an analysis of biological markers with regard to risk classification is to be performed. Furthermore, to create new protocols for patients with rare renal tumors, international collaboration with Children's Oncology Group and International Society of Pediatric Oncology is necessary.
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