Fetal rhabdomyomatous nephroblastoma: a tumour of good prognosis but resistant to chemotherapy.

Fetal rhabdomyomatous nephroblastoma (FRN) is a rare variant of Wilms' tumour. The tumour chiefly consists of fetal striated muscle with particularly distinct striations and central nuclei. To determine the effect of (preoperative) chemotherapy in the treatment of this subtype of nephroblastoma, a retrospective analysis was performed. By 1 November 1991, SIOP 9 had registered 852 patients (pts) from 55 centres. We report on 13 children diagnosed with FRN between 1988 and 1992 with a median age of 2 years and 1 month (range 1 month-8 years 6 months). There were 7 boys and 6 girls. 9 patients were classified as stage I, 2 as stage II, 1 as stage III and 1 as stage V. 12 patients received preoperative chemotheraphy with actinomycin-D and vincristine for 2 weeks (1 pt), 4 weeks (5 pts) and 8 weeks (6 pts) respectively. The average tumour volume at registration (determined by ultrasonography) in 12/13 patients was 965 cm3 (range 17.3-2520 cm3). 3/7 of the FRN patients showed no tumour regression after 4 weeks preoperative CT and 4/8 after 8 weeks preoperative chemotheraphy (compared with only 28 and 34%, after 4 and 8 weeks CT, of all trial patients). Of 13 patients, 10% are alive and free of disease with a mean follow up of 4 years. This variant of Wilms' tumour is a poor responder to preoperative chemotherapy and is associated with a generally favourable outcome in most of all unilateral cases when treated by surgery.