Paediatric renal tumours: an update on challenges and recent developments.

Paediatric renal tumours include a broad range of neoplasms which largely differ, but also overlap to a smaller extent, with adult kidney cancer. These include the embryonal tumour nephroblastoma, which accounts for the majority of cases of kidney cancer in the first decade of life and, despite boasting a cure in ~ 90% cases, still presents clinical challenges in a small proportion of cases. A variety of less common mesenchymal tumours, including the mostly indolent congenital mesoblastic nephroma, clear cell sarcoma of kidney which continues to be associated with poor outcomes for higher stage disease, and the typically lethal malignant rhabdoid tumour, form the bulk of the remaining presentations in the first decade. All three of these represent the intrarenal form of a wider 'family' of genetically related and histologically overlapping entities occurring in soft tissue and other anatomical locations. The latter two are examples of aggressive 'epigenetic' tumours driven by dysregulation of chromatin. In the second decade of life, renal cell carcinoma dominates, and with molecular characterisation many distinct subtypes are now described. Herein we discuss the developments in relation to diagnostic categorisation of paediatric renal cancers and how deeper understanding of the underlying biology is already providing therapeutic opportunity, while also focussing on the challenges that remain for the pathologist.