Pediatric Small Renal Masses: Can Tumor Size Predict Histology and the Potential for Nephron-sparing Surgery?

PURPOSE: The majority of children with unilateral renal masses suspicious for malignancy undergo radical nephrectomy, while nephron-sparing surgery is reserved for select cases. We investigated the impact of tumor size on the probability of histology. We hypothesized that pediatric small renal masses are more likely benign or non-Wilms tumor, thus potentially appropriate for nephron-sparing surgery. MATERIALS AND METHODS: The SEER (Surveillance, Epidemiology, and End Results) database was analyzed for patients aged 0-18 years diagnosed with a unilateral renal mass from 2000-2016. Statistical analysis was performed to help determine a tumor size cut point to predict Wilms tumor and assess the predictive value of tumor size on Wilms tumor histology. Additionally, a retrospective review was performed of patients 0-18 years old who underwent surgery for a unilateral renal mass at a single institution from 2005-2019. Statistical analysis was performed to assess the predictive value of tumor size on final histology. RESULTS: From the SEER analysis, 2,016 patients were included. A total of 1,672 tumors (82.9%) were Wilms tumor. Analysis revealed 4 cm to be a suitable cut point to distinguish non-Wilms tumor. Tumors ≥4 cm were more likely Wilms tumor (OR 2.67, P ≤ .001), but this was driven by the statistical significance in children 5-9 years old. From the institutional analysis, 134 patients were included. Ninety-seven tumors (72.3%) were Wilms tumor. Tumors ≥4 cm had higher odds of being Wilms tumor (OR 30.85, P = .001), malignant (OR 6.75, P = .005), and having radical nephrectomy-appropriate histology (OR 46.79, P < .001). CONCLUSIONS: The probability that a pediatric unilateral renal mass is Wilms tumor increases with tumor size. Four centimeters is a logical cut point to start the conversation around defining pediatric small renal masses and may help predict nephron-sparing surgery-appropriate histology.