Diagnostic accuracy and safety of renal tumour biopsy in patients with small renal masses and its impact on treatment decisions.

OBJECTIVE To assess the safety and diagnostic accuracy of renal tumour biopsy (RTB) in patients with small renal masses (SRM) and to assess if RTB prevents overtreatment in patients with benign SRM. MATERIAL AND METHODS In a retrospective, single-centre study from Västmanland, Sweden, 195 adult patients (69 women and 126 men) with SRM ≤ 4 cm who had undergone RTB during 2010-2023 were included. The median age was 70 years (range 23-89). The sensitivity, specificity and predictive values of RTB were calculated using the final diagnosis as the reference standard. Treatment outcomes were recorded for a median 42-month follow-up. Complications following the biopsies were assessed according to the Clavien-Dindo system. RESULTS The overall sensitivity of RTB was 95% (95% confidence interval [CI] 90% - 98%) and specificity was 100% (95% CI 95% - 100%). The positive predictive value was 100% and negative predictive value was 92%. The rate of agreement between RTB and the final diagnosis measured using kappa statistics was 0.92. Of the 195 patients, 62 underwent surgery and 48 were treated with ablation. The concordance rate between the RTB histology and final histology after surgery was 89%. Treatment was withheld in 67 of 195 patients with a benign or inconclusive RTB. No patients developed renal cell carcinoma or metastasis during follow-up. Complications occurred in two patients that were classified with Clavien-Dindo grades I and IV. CONCLUSIONS Percutaneous renal tumour biopsy appears to be a safe diagnostic method that provides accurate histopathological information about small renal masses and reduces overtreatment of benign SRM.