Undifferentiated sarcoma of the kidney: a tumor of childhood with histopathologic and clinical characteristics distinct from Wilms' tumor.

The pathological and clinical features of 123 patients with Wilms' tumor diagnosed between 1961 and 1977 were analyzed. A subgroup of nine patients with distinctive histology characterized by the presence of exclusively sarcomatous elements was identified. These patients were indistinguishable clinically from the other patients with Wilms' tumor and were treated as Wilms' tumor. The rate of recurrence in this group of sarcomatous Wilms' tumor was very high (7/9) and long-term disease-free survival correspondingly low )3/9 free of disease from 15 months to nine years) when compared to the patients with classical Wilms' tumor (50% recurrence rate and 71% currently free of disease). In addition, patients with metastases (seven of seven patients with recurrence had skeletal involvement as contrasted to one of 50 patients with metastatic classical Wilms' tumor). We conclude that the "sarcomatous Wilms' tumor" represents a distinct clinicopathological entity identifiable morphologically at diagnosis, best described as renal sarcoma and that in the future optimal treatment of this disease may vary somewhat from the treatment of classical Wilms' tumor.