Immune Checkpoint Inhibitor-Induced Sarcoidosis-Like Reaction Mimicking Pulmonary Metastasis: A Case Report.

Immune checkpoint inhibitors can induce sarcoidosis-like reactions that mimic disease progression and pose diagnostic challenges. We report a case of a 77-year-old woman who developed pulmonary nodules during pembrolizumab therapy for recurrent uterine carcinosarcoma. Despite radiologic suspicion of metastatic disease, systemic tumor control was maintained. Thoracoscopic wedge resection revealed non-caseating granulomas without evidence of malignancy or infection, confirming a sarcoidosis-like reaction. Pembrolizumab therapy was continued without corticosteroid treatment, and the patient remained disease-free three years after treatment completion. This case highlights an important diagnostic pitfall during immune checkpoint inhibitor therapy. Sarcoidosis-like reaction should be considered in the differential diagnosis of newly developed pulmonary lesions, and histologic confirmation is essential to avoid misdiagnosis and inappropriate discontinuation of effective immunotherapy.