Cytodifferentiation of a Wilms' tumor pulmonary metastasis: theoretic and clinical implications.

BACKGROUND: Complete maturation (cytodifferentiation) of treated metastatic Wilms' tumor is an infrequent occurrence. In a large series of reports, Wilms' metastases have generally contained malignant blastemic elements admixed with lesser amounts of cytodifferentiated mesenchyme. The authors describe a patient in whom complete maturation of a pulmonary metastasis was documented after intensive chemoradiotherapy.

METHODS: A MEDLINE search was employed to identify pertinent cases from 1966 to the present. Key words used in the search included Wilms' tumor, relapse, therapy, metastasis, maturation, and cytodifferentiation. Four patients were identified as having completely mature cytodifferentiated pulmonary metastases of Wilms' tumor after chemotherapy; one had also undergone irradiation of the pulmonary metastasis.

RESULTS: The primary tumor was an extremely necrotic blastemic Wilms' tumor devoid of maturation, as studied after irradiation and chemotherapy. The lung metastases (examined 13 years later) were represented by a scar and a nodule comprised of bland epithelium and tubules admixed with mature smooth muscle. Immunohistochemical stains, used to assess the proliferative rate of these cells, revealed a nearly negligible proliferation index.

CONCLUSIONS: This report suggests that therapy (chemotherapy and/or irradiation) may effect, on occasion, complete cytodifferentiation of Wilms' tumor pulmonary metastasis. Although this would appear to be an uncommon event, its true incidence is unknown, because few patients with metastatic pulmonary Wilms' tumor are subjected to biopsy. The findings of this study suggest that for children with radiologically stable Wilms' lung metastases (as determined by imaging studies) who are yet undergoing intensive chemoradiotherapy, the notion of a surgical biopsy should be entertained to determine the true nature of the radiologic images. For some, this might result in the cessation of further therapy that would be unnecessary and not without complications.