Blastemal histology in chemotherapy-treated pediatric Wilms tumors (nephroblastoma) is associated with adverse prognosis. To uncover the underlying tumor biology and find therapeutic leads for this subgroup, we analyzed 58 blastemal type Wilms tumors by exome and transcriptome sequencing and validated our findings in a large replication cohort. Recurrent mutations included a hotspot mutation (Q177R) in the homeo-domain of SIX1 and SIX2 in tumors with high proliferative potential (18.1% of blastemal cases); mutations in the DROSHA/DGCR8 microprocessor genes (18.2% of blastemal cases); mutations in DICER1 and DIS3L2; and alterations in IGF2, MYCN, and TP53, the latter being strongly associated with dismal outcome. DROSHA and DGCR8 mutations strongly altered miRNA expression patterns in tumors, which was functionally validated in cell lines expressing mutant DROSHA.

The prognosis of children with primary Wilms' tumor lung metastases mainly depends on the biology of primary tumors and metastases and is excellent with adequate treatment. Pulmonary metastasectomy is indicated if complete remission can be achieved to avoid lung irradiation. In the future a standardized local approach to nonresponding lung metastases (metastasectomy, irradiation, or both) will have to be prospectively evaluated regarding outcome, acute toxicity, and late effects.

Structuring the treatment of progressive nephroblastoma as well as introducing new drugs have improved the outcome significantly. However improvement is depending on the specific risk profile. Very high risk tumours are often resistant to conventional treatment, hence an international uniform treatment concept is needed to achieve conclusive results in this small group.

Malignant non-Wilms renal tumors (NWRT) are a small but relevant subgroup of renal neoplasms in children. In this study we analyzed corresponding data from the trials SIOP 93-01/GPOH and SIOP 2001/GPOH of the Society of Pediatric Oncology and Hematology.Data of 22 patients with NWRT and primary lung metastases were retrospectively reviewed. Analyses included epidemiology, tumor characteristics, chemotherapy, local treatment, and outcome.The following diagnoses were registered: Malignant Rhabdoid tumor of the kidney (MRTK, n=15), Renal-cell carcinoma (RCC, n=3), Clear-cell sarcoma of the kidney (CCSK, n=3), and primitive neuro ectodermal tumor (PNET, n=1). Median age of patients at diagnosis was 14 months. Overall survival was 36.36% (8/22). Of the 15 children with MRTK 3 survived, 3/3 patients with RCC, 1/3 patients with CCSK, and 1/1 patient with PNET survived. Lung metastases disappeared in 6 patients after initial chemotherapy, 6/8 patients undergoing local treatment of lung metastases (surgery, irradiation, or both) achieved complete remission. Only patients with complete clearance of lung lesions, either through neoadjuvant chemotherapy or subsequent local treatment, survived. Mean Follow up was 31 months (1-137).Survival of patients with stage IV NWRT is dismal. Complete removal of lung metastases seems mandatory for survival. An aggressive diagnostic and therapeutic approach seems justified in affected children.

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