Introduction:

Increased utilization of imaging modalities has led to a rise in the diagnosis of incidental small renal masses. Partial nephrectomy (PN) has been established as the gold standard treatment modality for majority of these T1 tumors, as it offers excellent oncologic outcomes and preserves renal function. Over the past decade and a half, advances in imaging have not only led to an earlier detection of these masses, but also an improved ability to differentiate benign renal masses such as lipid poor AMLs and benign complex renal cysts. With the increasing utilization of active surveillance, renal mass biopsy along with improved imaging, we examined the incidence of benign pathology at the time of partial nephrectomy in a contemporary cohort of patients undergoing PN for presumed renal cell carcinoma (RCC).

Methods:

We performed a chart review on a prospectively maintained database on a series of patients who underwent PN between January 1^st 2006 and December 31^st, 2019 for suspected RCC. Patients with cystic renal masses or definitive benign pathology on pre-operative imaging were excluded from analysis. Pre-operative characteristics for patients with benign and malignant pathologies were collated. Trends in the incidence and type of benign pathology (oncocytoma or AML) were analyzed. Statistical analysis was performed using Student’s T test for continuous variables, Chi-Squared for categorical variables, and univariate linear regression for trendlines.

Results:

A total of 1083 patients met inclusion criteria, with 210 patients (19.4%) identified to have benign disease on final pathology. Of patients with benign disease, 49 patients (23%) had AML and 135 patients (64%) had oncocytoma. On univariate analysis, patients who had benign pathology were more likely to be female (46% vs 28%, p<0.001), have a tumor size ≤

4 cm (85% vs 79%, p<0.05) and more likely to have multifocal disease (8% vs 5%, p<0.01). Age (62.5 vs 61.3 years), BMI (28 vs 29), and rates of pre-operative MRI (65% vs 67%) were comparable between benign vs malignant groups. When reviewing PN pathology between 2006 to 2019, there was a significant increase in the incidence of benign pathology (R²=0.29, p<0.05). When examining 3-year rolling averages over this same time period, the incidence of oncocytoma increased (51% to 59%) while the incidence of AML decreased (49% to 30%).

Conclusion:

The overall incidence of benign pathology in this contemporary cohort of patients undergoing PN for presumed RCC did not decline over time. Despite improvements in imaging as well as increased utilization of renal mass biopsy and active surveillance, benign renal masses, particularly oncocytoma, continue to pose a diagnostic challenge in patients with solid small renal masses.

Funding: N/A