Pediatric cystic nephromas: distinctive features and frequent DICER1 mutations.

Cystic nephromas (CNs) are uncommon benign renal neoplasms that present with a bimodal age distribution, affecting either infants/young children or adult females. Although differences between these age groups have been suggested, large studies of pediatric CN have not been conducted. As a result, the nomenclature and diagnostic criteria for these lesions remain controversial. In addition, the morphological overlap seen between CN and cystic partially differentiated nephroblastoma (CPDN) can result in diagnostic dilemmas. This study reviews the morphologic and radiographic features of 44 pediatric CN prospectively enrolled on a Children's Oncology Group protocol from 2007 to 2013. Although the typical multicystic architecture with thin septa described in adult CN was present in all of our pediatric cases, differences were also identified. We report distinctive features that add to the morphological spectrum of CN in children. Of the 44 cases, 16 had been previously analyzed and reported for DICER1 mutation, and either loss of function or missense mutations or both were identified in 15 of 16. In contrast, we analyzed 10 cases of adult CN, and all were negative for DICER1 mutations; similarly, 6 CPDNs previously analyzed and reported were negative for DICER1 mutations. Therefore, the clinical, morphological, and genetic differences between pediatric and adult CN, as well as between CN and CPDN, suggest that these 3 lesions represent distinct entities.