Renal tumor biopsy to reduce overtreatment of renal oncocytomas.

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623 Background: Up to 30% of renal masses are benign tumours, the most common of which is renal oncocytomas (RO). Our practice is to offer renal tumour biopsy (RTB) for small renal masses (SRM; ≤4cm) as part of a multi-disciplinary pathway. Our objective was to determine whether RTB influenced the management of RO. Methods: Retrospective descriptive analysis of the management of all sporadic cases with a histological diagnosis of RO (biopsy or surgical) at a high-volume tertiary centre from January/2012 to June/2019. Results: 170 patients (66% male; median age 67 years; median age-related Charlson comorbidity index 3) were diagnosed with 177 RO (median size 36mm). 70% (124) of RO were diagnosed using tumour biopsy (median size 33mm), of which 116 (93.4%) embarked on active surveillance (AS; 101) or watchful waiting (15). 53 (30%) RO were diagnosed after surgical excision (median size 50mm; 15 partial and 38 radical nephrectomies), of which 4 lesions were initially managed with AS. Median follow-up on AS was 20 months (2 to 84 months), with a median decrease in estimated glomerular filtration rate of 3 ml/min/1.73m2 over this period. 79% of RO on AS were SRMs. Median overall lesion size change was 1.1mm/year during follow up. Overall 62.6% of lesions grew, a quarter of which at a rate >5mm/year. Nine cases of RO on AS changed to intervention due to lesion growth or patient choice. No metastases were reported in the whole cohort. Three patients on AS died (stroke, respiratory arrest secondary to food inhalation, and unknown cause). One patient who had had surgical excision of RO died of unknown cause. Conclusions: Surgical risks for benign renal lesions are not different to those taken for renal cell carcinoma. RTB reduces the use of unnecessary surgery and its incumbent morbidity for benign renal lesions, such as RO. AS is a safe management option for patients with RO and can be used to reduce overtreatment-associated harm.