Pitfalls in the differential diagnosis of renal tumor in an adolescent.

The differential diagnosis of renal tumors, particularly in adolescents, may be challenging. We describe an 11-year-old female with a primary intra-renal mass. Initial differential diagnoses included primitive neuroectodermal tumor (PNET), desmoplastic small round cell tumor (DSRCT), and Wilms Tumor (WT). Extensive pathologic and molecular analysis on initial and relapsed tumor samples confirmed WT. The EWS-WT1 and EWS-FLI1 rearrangements, distinctive of DSRCT and PNET were negative. The differential diagnosis on monophasic blastemal WT may be complex. Primary renal DSRCT and PNET have been rarely described. Nevertheless, molecular confirmation for these rare conditions may be necessary in selected cases.