Pembrolizumab-Induced Tubulointerstitial Nephritis in Early-Stage Triple-Negative Breast Cancer: A Case Report.

Immunotherapy has become an integral part of cancer treatment, with immune checkpoint inhibitors (ICIs) increasingly used across multiple tumor types, including early-stage triple-negative breast cancer. However, these therapies can trigger immune-related adverse events (irAEs) that may involve various organ systems. We report a case of acute tubulointerstitial nephritis (ATIN) secondary to pembrolizumab in a woman in her 50s treated for early-stage triple-negative breast cancer. After three cycles of neoadjuvant chemotherapy combined with pembrolizumab, the patient presented with acute kidney injury (AKI) and elevated inflammatory markers. Infectious, obstructive, and other secondary causes were excluded. A kidney biopsy was performed, with findings consistent with ATIN, most likely pembrolizumab-induced. Pembrolizumab was discontinued, and corticosteroid therapy (prednisolone 0.5 mg/kg/day) led to rapid improvement and near-complete recovery of renal function. This case highlights the importance of early recognition and prompt management of ICI-related AKI to prevent irreversible kidney damage.