[Paediatric kidney tumours: Update on the challenges of nephroblastoma and other kidney tumours]

In 85% of cases, kidney tumours in children are represented by nephroblastoma or Wilms' tumour. Children are treated according to protocols developed by SIOP-RTSG in Europe and several other continents and by NWTSG-COG in North America. The SIOP-RTSG protocol includes upfront chemotherapy, usually without biopsy, followed by nephrectomy, which must be performed rigorously, precisely and according to a protocol by the pathologist in order to classify the tumour into its appropriate risk group (low risk, intermediate risk or high risk) and to assess its local stage of extension (stage 1, 2 or 3). These criteria will determine the choice and duration of post-operative chemotherapy, with or without radiotherapy. The molecular abnormalities of nephroblastoma are heterogeneous, involving several chromosomal regions such as 1p, 16q, 1q, 11p15 and several genes such as WT1, CTNNB1, WTX, SIX1/2, DROSHA/DGCR8, TP53, MYCN, FBXW7 and TRIM28. Analyses are underway to determine whether these molecular abnormalities associated with the absolute volume of chemoresistant blastema could help divide children into different groups. In 15% of cases, these are tumours other than nephroblastoma, very different from one another, with a highly variable prognosis ranging from benign tumours such as nephrogenic rest, paediatric cystic nephroma and metanephric tumour to very aggressive tumours such as rhabdoid tumour of the kidney or medullary carcinoma of the kidney. In this group, each tumour has its own genetics, whose molecular mechanisms are increasingly well understood, with fusions, tandem duplications or gene mutations which can help the pathologist to achieve to an accurate diagnosis in each morphological context. In some situations, the identification of these molecular alterations may lead to a targeted treatment.