Wilms tumor in horseshoe kidneys: a report from the National Wilms Tumor Study.

An analysis of information on 2,961 patients with Wilms tumor entered in the National Wilms Tumor Study up to July 1983 revealed 13 tumors occurring in horseshoe kidneys. The correct preoperative diagnosis was made in 6 of the 13 patients. At presentation 5 patients had stage 1, 3 stage 2 and 5 stage 3 disease. Major preoperative or intraoperative tumor spillage occurred in 3 patients. The over-all survival rate was 85 per cent after a mean followup of 45 months. The surgical, pathological and therapeutic aspects of Wilms tumor in horseshoe kidneys were analyzed carefully. The frequency of horseshoe kidneys in patients with Wilms tumor registered with the National Wilms Tumor Study was determined and was used in conjunction with population data to estimate the relative risk of Wilms tumor occurrence in children with horseshoe kidneys.