Extrarenal Wilms’ Tumor: Challenges in Diagnosis, Embryology, Treatment and Prognosis

ABSTRACT

Wilms’ tumor is one of the most common childhood solid malignancies, which classically arises from primitive metanephric cells, but exceptionally it may arise in places other than kidneys. Extrarenal Wilms’ tumor is a rare but challenging entity, considering its diagnosis, histopathology, staging, treatment, and prognosis. Diagnosis of extrarenal Wilms’ tumor is always postsurgical, which may jeopardize treatment planning and consulting with parents in the first step. The histopathology of Wilms’ tumor is very confusing. While most authors believe that it arises from primitive ectopic nephrogenic rests, teratoid Wilms’ tumor leads to the debate whether this tumor is neoplastic or embryonic. Staging of extrarenal Wilms’ tumor is also a challenge when we consider the National Wilms’ Tumor Study (NWTS) recommendations; all these tumors should be considered as stage II or higher as they are beyond the renal capsule. This will mandate chemotherapy for all patients while most of the reported cases have a favorable histology, and long-term tumor-free survival has been reported even with exclusive surgery in some case reports. Although treatment strategies for extrarenal Wilms’ tumor are the same as those for renal Wilms’ tumor, different locations and neighboring organs may invoke special considerations and scenarios while planning for surgery and adjuvant therapies. Consulting with the parents is also a problem, considering the rarity of the disease and limited publications. In this chapter, we discuss all these topics in detail after a systematic review of extrarenal Wilms’ tumor cases to date in order to provide a clear perspective for confronting this rare disease.