Drug-Induced Kidney Injury Caused by Osimertinib: Report of a Rare Case.

Tyrosine kinase inhibitors (TKIs) that target the epidermal growth factor receptor (EGFR) have shown highly favourable outcomes in patients with advanced-stage non-small-cell lung cancer (NSCLC). The adverse effects of EGFR-TKIs are generally less severe than those of conventional cytotoxic therapies. We report a patient with NSCLC who presented with acute kidney injury associated with biopsy-proven acute tubular injury during osimertinib treatment and whose renal function recovered after reducing the osimertinib dose. A 61-year-old male smoker complained of dyspnoea on exertion for 1 month before his visit to the medical centre. He was diagnosed with lung adenocarcinoma of the left lower lobe (cT4N3M1a, stage IVA) and was positive for an EGFR mutation (exon 19 deletion). Osimertinib was initiated at 80 mg/day. At treatment initiation, the patient's serum creatinine level was 0.64 mg/dL, with microscopic haematuria; by day 83, this level had increased to 1.33 mg/dL, with proteinuria. On day 83, we reduced the osimertinib dose to 40 mg/day and performed a kidney biopsy on day 98. The histological diagnosis was tubular injury with IgA deposition. Based on the clinical course and histological findings, we speculated that the kidney injury was associated with osimertinib. After dose reduction, the patient's serum creatinine level decreased to 1.07 mg/dL, and proteinuria disappeared. He maintained a partial response for >6 months after osimertinib administration. We report the first case of biopsy-proven mild IgA deposition, crescent formation, and tubular injury probably caused by osimertinib and demonstrate how reducing the osimertinib dose could strike a balance between its anti-cancer efficacy and adverse effects.