Kidney Biopsy in Cancer Patients With Acute Kidney Disease: Histological Findings and Kidney Outcomes.

Background and aims The incidence and prevalence of acute kidney disease (AKD), including acute kidney injury (AKI) and proteinuria, are increased in cancer patients. This study aimed to investigate the variety of renal histopathological lesions in cancer patients and their associations with systemic anticancer therapies (SACT) before and after 2017, the year when new SACTs like immune checkpoint inhibitors and target therapies were generally introduced, as well as the role of kidney biopsy (KB) in guiding treatment decisions. Material and methods This retrospective cohort study included adult cancer patients who underwent kidney biopsy for AKD at a single center over a 14-year period. Clinical, laboratory, and renal histopathological data were collected, and therapeutic options were evaluated. The study cohort was stratified into three groups - (i) SACT-related AKD, (ii) cancer-related AKD, and (iii) non-SACT/non-cancer-related AKD - based on clinical judgment by the treating nephrologist, allowing detailed characterization of AKD patterns. Results Fifty-five patients (61.8% men; mean age 64.7±9.9 years) were included. At diagnosis, median serum creatinine was 2.2 mg/dl (interquartile range (IQR) 1.6-4) and proteinuria 1.3 g/24h (IQR 0.25-4). Most patients (63.6%) were receiving SACT. Glomerulopathies were the most frequent lesions (43.6%), with focal segmental glomerulosclerosis (FSGS) predominating (29%). Acute interstitial nephritis (AIN), acute tubular injury (ATI), and mixed AIN/ATI were identified in 21.8%, 12.7%, and 9.1% of cases, respectively, while renal tumor infiltration occurred in 7.3%. AKD was attributed to SACT in 41.8%, most commonly immunotherapy (52.2%), and AIN was the prevailing lesion (82.6%). A significant shift in histopathological patterns was observed after 2017 (p=0.006), with higher frequencies of glomerulonephritis (51.3% vs. 25%) and acute tubulointerstitial nephritis (25.6% vs. 12.5%). Among patients receiving targeted treatment based on KB findings, including corticosteroid therapy, all experienced favorable renal outcomes. Conclusions This study highlights the expanding spectrum of kidney injury in cancer patients, the influence of modern SACT on renal pathology, and the critical role of kidney biopsy in guiding individualized management strategies.