What happened, in summary

A 78-year-old Japanese man with advanced lung adenocarcinoma began first-line treatment with pembrolizumab, cisplatin, and pemetrexed. He was also taking rabeprazole. Thirty days after the first treatment, persistent diarrhea led to hospital admission. His creatinine had risen from 0.84 to 1.99 mg/dL, with protein and blood detected in the urine.

The team initially considered dehydration from diarrhea and gave intravenous fluids. His kidney function continued to deteriorate, however, and creatinine reached 3.34 mg/dL. A kidney biopsy showed severe acute tubular injury together with interstitial nephritis. The combination of chemotherapy, immunotherapy, diarrhea, and other medicines made it difficult to identify one single cause.

All cancer treatment was stopped, but the kidney injury continued to worsen. Prednisone was started at 60 mg daily and gradually tapered over six months. During follow-up, creatinine stabilized at approximately 1.1–1.3 mg/dL, with mild persistent proteinuria.

After his kidney function became more stable, he began a modified cancer regimen containing SAR408701. His course shows how serious kidney injury can develop rapidly during combined chemotherapy and immunotherapy and why biopsy was important in guiding prolonged corticosteroid treatment.