The Fate (Outcome) of Clinically Apparent Single Lesion and Oligofocal Nephroblastomatosis Treated According to SIOP/GPOH Protocols for Wilms Tumor.

Background The management of clinically apparent single lesions or oligofocal nephroblastomatosis, a facultative precursor of nephroblastoma, remains debated.Methods We retrospectively analyzed 37 patients with clinically apparent single or oligofocal nephroblastomatosis (two to three lesions per kidney) among 2347 patients registered between 1993 and 2014 in the SIOP93-01/GPOH and SIOP2001/GPOH renal tumor studies.Results Of the 37 patients, 23 had a single lesion, and 14 had oligofocal disease; 65% had a clinically apparent and/or molecularly diagnosed cancer predisposition syndrome, and 27% bilateral involvement. Preoperative chemotherapy was administered to 62%, primary surgery to 32%, and chemotherapy without surgery to 5%. Nephron-sparing surgery was performed in 71%. In oligofocal cases, preoperative chemotherapy led to significant tumor volume reduction. Prognosis was favorable: 10-year event-free, nephroblastoma-free, and overall survival rates were 77.4%, 80.7%, and 92.0%, respectively. Of 35 patients who underwent definitive surgery, 26 received short postoperative treatment (≤4 weeks) or a watch-and-wait approach (W&W). Three patients (11.5%) developed nephroblastoma, two of whom were successfully salvaged. Ten-year nephroblastoma-free survival was 74.1%, 90.0%, and 100% for short, W&W, and long postoperative treatment (>4 weeks), respectively. All 12 patients undergoing primary definitive surgery remained nephroblastoma-free.Conclusion Short postoperative chemotherapy or W&W is a safe option for patients with single or oligofocal nephroblastomatosis in complete remission, provided they undergo close ultrasound monitoring. The modest relapse risk, manageable with salvage therapy, must be weighed against the toxicity of prolonged treatment, especially in infants. Both primary and delayed surgery are viable strategies.