Renal tumours of childhood: what's new in classification, morphology, molecular findings and prognosis

Despite being one of the most frequent solid tumours in children, renal tumours are uncommon. Their accurate diagnosis and staging are essential for the appropriate treatment because they comprise a variety of entities with a broad spectrum of clinical, histological, molecular biology, and prognostic features. Wilms tumour (WT) accounts for 80–85% of renal tumours of childhood, whereas other tumours including mesoblastic nephroma, clear cell sarcoma, rhabdoid tumour, renal cell carcinoma, and others are extremely uncommon (up to 2%–4% each), which explains why they pose a significant diagnostic challenge for pathologists. There are two major study groups with different treatment approaches but very comparable outcomes. The International Society of Paediatric Oncology approach (followed in most of the world) is based on preoperative chemotherapy, followed by surgery and further therapy, whereas the Children's Oncology Group approach (followed mainly in the United States and Canada) is based on primary surgery, followed by postoperative treatment. In both study groups for WT the most important prognostic factors are histological type and stage. The criteria for subtyping and staging are similar but still differ between the study groups, making a direct comparison impossible, but nevertheless, the outcomes are remarkably similar. The chapter provides an update on pathology, recent molecular discoveries and prognosis in paediatric renal tumours.