Abdominal relapses in irradiated second National Wilms' Tumor Study patients.

Ten of 259 (3.8%) irradiated patients with group 2 and 3 tumors in the second National Wilms' Tumor Study experienced initial clinical relapse either in the operative site or elsewhere in the abdomen, excluding the liver and opposite kidney. Analysis of factors associated with abdominal recurrences has shown the independent significance of unfavorable histology, field size of the radiotherapy portals, and a postoperative delay of ten or more days before starting irradiation.