Isochromosome 7q in adult Wilms' tumors: Diagnostic and pathogenetic implications

Wilms' tumors affecting adults are rare and are thought to have a worse pro gnosis than similar stage tumors in the pediatric population. To understand these turners better, the authors reviewed their multi-institutional exper ience in a series of nine lesions diagnosed as Wilms' tumors in adults. In addition to histologic and immunohistochemical examination, they performed cytogenetic analysis and fluorescence in situ hybridization. On review, fou r cases were reclassified: two "blastema only" as Ewing's sarcoma/primitive neuroectodermal tumor and the other two as clear cell sarcoma of soft part s and sarcoma not otherwise specified (NOS). Of the remaining five cases, t hree exhibited biphasic histology and two were triphasic. In this group, th ere were three women and two men, and patient age ranged from 17 to 37 year s (median age, 26 years). Tumor size was large and ranged from 10 to 31 cm (median tumor size, 12.5 cm). Histologically, the tumors showed the typical features of Wilms' tumors with varying amounts of blastema (n = 5), epithe lium (n = 5), and stroma(n = 2). No tumors contained anaplasia, and persist ent renal blastema was not identified in the non-neoplastic kidney in any s pecimen. All tumors were positive fur cytokeratins (CK7, n = 3; pankeratin, n = 5), and one tumor was weakly positive for CD99 (O-13). Molecular analy sis including dual color fluorescence in situ hybridization (all tumors), a nd cytogenetic analysis (n = 2) disclosed the presence of isochromosome 7q in three of five tumors whereas all tumors were diploid with respect to chr omosome 12, Follow-up data ranged from 6 to 133 months (median follow-up, 8 2 months) with progression in only one patient who had stage TV disease wit h lymph node and lung metastases at presentation. The authors conclude that adult Wilms' tumor has been overdiagnosed. Most "blastema-only" tumors in adults are not Wilms' tumors, and in an adult, biphasic morphology should b e the minimum criteria for their diagnosis. Using strict diagnostic criteri a, adult Wilms' tumors have a relatively favorable prognosis. The character istic Endings of isochromosome 7q, lack of trisomy or tetrasomy for chromos ome 12, and absence of persistent renal blastema suggest that the pathogene sis of Wilms' tumors in adults may be different than in the pediatric popul ation. These genetic features may be helpful in distinguishing adult Wilms' tumors from other primary renal tumors.