Biopsy and identification of risk factors for discordance in renal tumor: results from the BIRD study (UroCCR n°230).

PURPOSE: To assess the rate of histological discordance between renal mass biopsy(RMB) and final surgical pathology in patients with localized renal tumors, and to identify risk factors of discordance. MATERIALS AND METHODS: The BIRD study is a retrospective multicenter analysis conducted within the prospective UroCCR database between February 2004 and January 2025. We included all patients who underwent a renal mass biopsy followed by surgical treatment(partial or radical nephrectomy). The primary endpoint was the histological discordance rate, defined as a mismatch in tumor type between the biopsy and the surgical specimen, or a non-diagnostic biopsy, and diagnostic accuracy. Univariate and multivariate logistic regression analyses were performed to identify factors associated with discordance. RESULTS: A total of 1,301 patients from 19 centers were included, with 65% male and a median age of 63 years(51-71). Tumors were equally distributed between the right and left kidneys, with a median size of 3.7 cm(2.5-5.0). Final histology showed 8% benign and 92% malignant tumors. Tumor necrosis was found in 23% of cases. Among tumors assessed for nuclear grade, a 48% discordance was observed between low(ISUP1-2) and high grades(ISUP3-4). Overall, the histological discordance rate was 18%, including 3.7% for malignancy diagnosis, 8.4% for histological subtype, and 5.7% for non-diagnostic biopsies. On multivariable analysis after multiple imputation, cystic tumor(OR 2.18, 95%CI 1.23-3.85, p = 0.007) was independently associated with increased risk of histological discordance. Moderate and high R.E.N.A.L. score complexity were associated with reduced discordance risk(OR 0.67, 95%CI 0.47-0.96, p = 0.03 and OR 0.60, 95%CI 0.37-0.98, p = 0.04, respectively). CONCLUSIONS: RMB provided a high diagnostic yield but was associated with an overall 18% discordance rate. Cystic tumors were the only independent factor associated with an increased risk of discordance, while tumor complexity and size influenced discordance subtypes. Regarding ISUP grade, RMB showed imperfect reliability, failing to reflect true tumor aggressiveness in nearly half of discordant cases.