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A mesenchymal tumor with the macroscopic and microscopic features of a fetal rhabdomyoma arose in the liver of a 14-year-old boy. Thirteen years previously this boy had been treated for a fetal rhabdomyomatous nephroblastoma with nephrectomy and--for subsequent peritoneal disseminations--with surgical excision, radiotherapy, and chemotherapy. The unusual hepatic location of the rhabdomyomatous tumor in this patient supports the view that this mature tumor developed from a metastasis of the original nephroblastoma. As such, this case may represent an example of irreversible change of a malignant process into a benign tumor probably caused by the action of systemic chemotherapy.

Interstitial proliferation of striated muscle cells in the lung is rare. A few cases in the literature only document infants with associated lung and other major organ anomalies incompatible with long-term survival. In this report we document a case of diffuse patchy interstitial proliferation of striated muscle cells in the left lung and confirm their nature by immunohistochemistry and electron microscopy. In particular, we show that these skeletal muscle cells express alpha-sarcomeric actin, but not alpha-smooth muscle actin, indicating an antigenetically well-developed striated muscle phenotype despite morphologically embryonal features.