Wilms tumor (WT) is the most common malignant renal tumor in children. Survival has improved with standardization of treatment from guidelines and clinical trials through the International Society of Pediatric Oncology and Children’s Oncology Group. While these groups take different approaches, surgical resection remains the mainstay of treatment.¹ Radical nephrectomy has been the standard of care, with nephron-sparing surgery (NSS) advocated for in cases of bilateral WT (BWT), multifocal unilateral disease, or those with Wilms predisposition syndromes.¹ NSS is aimed at preserving functional renal tissue and preventing long-term declines in renal function. While the 20-year risk of end-stage renal disease (ESRD) for unilateral WT is 0.7%, the 3-year risk of ESRD is 4% for patients with metasynchronous disease and 19% for patients with BWT.² For patients with BWT and metasynchronous disease, these high rates of ESRD are thought to be driven by aggressive disease in a solitary remaining kidney, which then requires further surgical excision to prevent progression or metastasis.² Aside from renal mass loss, nephrotoxic chemotherapy and radiation-induced kidney injury likely also contribute to declines in renal function in patients with WT.² Renal insufficiency has been tied to higher risk of cardiovascular disease, hospitalization, and death amongst adults³; hence NSS is increasingly a consideration in pediatric patients with renal malignancy.

Recent International Society of Pediatric Oncology protocols permit partial nephrectomy for select patients with unilateral WT.⁴ A meta-analysis of 66 studies comparing partial nephrectomy to radical nephrectomy for WT found equivalent rates of tumor rupture, tumor recurrence, and overall survival.⁵ However, the authors caution that patients selected for NSS were more likely to have lower-stage disease. With respect to renal function, a second meta-analysis of 20 studies demonstrated improved postoperative renal function for partial nephrectomy compared with radical nephrectomy.⁶ While tumor size and stage are reported in most of the included studies, interpretation is limited by our ability to make more detailed comparisons about the anatomic complexity of the renal masses, which in turn may have driven the decision to perform a NSS.⁶

While there is likely an expanding role for NSS in WT, this must be done so carefully, balancing the preservation of functional renal tissue with potential for increased complications, positive margins, and tumor recurrence. When considering NSS, nephrometry scores, which quantify multiple anatomic characteristics of a renal mass, can aid in surgical planning and decision-making. Nephrometry scores have been widely studied in adult tumors to quantify the risk of complications following partial nephrectomy with the R.E.N.A.L. (for radius, exophytic/endophytic, nearness of tumor to collecting system, anterior/posterior, location relative to polar line) score being the most used and best correlated with perioperative outcomes.⁷ In considering a nephron-sparing approach, nephrometry scores are one part of the decision. These scores can be coupled with 3 D models (Figure) to aid in surgical planning and intraoperative decision making.^1,8

Preliminary studies have applied this score to pediatric patients,⁹ but it is not widely utilized. Our group showed moderate-good agreement when multiple raters scored consecutive patients undergoing NSS using the R.E.N.A.L. nephrometry score.¹⁰ Additionally, the cohort’s median nephrometry score was 9, indicating intermediate-high complexity tumors undergoing NSS. Higher scores were associated with longer length of stay and operative time, but without a difference in 30-day complications.¹⁰ At 35-month follow-up, 78% remained cancer free, 17.9% had died, and 3.6% had a recurrence.

Currently, utilization of NSS has been surgeon and center specific. Widespread use of nephrometry scores would allow for improved analysis of this approach.¹⁰ As we seek to better understand how partial nephrectomy fits into the management paradigm for WT, standard use and reporting of nephrometry scores will be paramount for our community to compare mass complexity across institutional series. Nephrometry scores are easily reproducible and, much like adult urologic oncology literature, should be included in all reports to allow for more meaningful conclusions with the goal of improving outcomes for children with WT.