Introduction:

Renal mass biopsy (RMB) has been underused as a diagnostic tool due to the high rates of non-diagnostic biopsies (20%). Confocal Fluorescence Microscopy (CFM) allows for real-time imaging of specimens with detection of tissue alterations and its feasibility on RMB has been reported. Our study aimed to demonstrate the utility of ex vivo CFM on RMB in a daily urological practice. The primary endpoint was to evaluate the ability of CFM to discriminate between good/poor quality cores. The secondary endpoint was to assess the agreement between CFM and standard histopathology diagnosis for identification of tumoral features in RMB. 

Methods:

From May 2019 to May 2020, 18 RMB were performed at our institution and prospectively included in our study. RMB were performed following a state-of-the-art technique, with a minimum of 2 quality cores (at least 0.5 cm of length, not detached or torn) for each case. Specimens were first examined using a confocal scanning microscope after appropriate processing, within 15 minutes of biopsy. Renal tissue architecture was then assessed and reported as normal or as tumoral, fibrotic or necrotic when altered. If normal or insufficient tissue was reported, rebiopsy was instantly performed. After CFM imaging, all specimens underwent appropriate processing and were examined by a uro-pathologist. Clinicopathological features, surgical management and complications were reported. Descriptive analysis was performed. Continuous variables were reported as medians, and interquartile ranges (IQR). Qualitative variables were reported as frequencies and percentages (%).  

Results:

Median age at diagnosis of RM was 66 years old (IQR: 55-72), with a gender ratio (M:F) of 13:5. Median tumor size was 2.5 cm (IQR: 2.2-4.2). Renal mass staging was cT1a in 10 patients (55%) and cT1b in 8 patients (44%). Median RENAL score was 7 (IQR:5-8). Standard histopathologic analysis of biopsies revealed oncocytoma in 5 cases (28%), clear cell RCC (ccRCC) in 9 cases (50%), non-ccRCC in 3 cases (17%) and urothelial carcinoma in 1 case (6%). All the biopsy core specimens, previously examined by CFM, were sufficient for standard histologic analysis. Real time identification of normal tissue by CFM led to instant rebiopsy in one patient. The overall detection rate of tumoral tissue by CFM was 100%, in agreement with histopathologic analysis. The median percent of tumor involvement in confocal specimens was 70% (IQR 30-80). No patient experienced complications related to RMB in our cohort. 

Conclusion:

CFM was able to identify core quality in 100% of cases. We reported a diagnostic accuracy of 100% for CFM, in agreement with histopathologic analysis. This supports our hypothesis that CFM performed at the time of RMB instantly discriminates between normal/tumoral tissue. This would benefit our clinical practice by decreasing the odds of non-diagnostic biopsies and subsequent need for rebiopsy. 

Funding: N/A