Sarcoid-like Reaction With Pleural Involvement After Neoadjuvant Chemo-immunotherapy For Lung Cancer

We report a patient with stage IIA (cT2bN0M0) lung adenocarcinoma who developed new diffuse pleural, pulmonary, and nodal FDG uptake on ¹⁸ FDG-PET/CT after three cycles of neoadjuvant nivolumab plus cisplatin–pemetrexed, with slight regression of the primary tumour. These findings raised the diagnostic dilemma between disease progression and immune checkpoint inhibitor (ICI)-related sarcoid-like reaction (SLR). Rapid clinical and metabolic improvement after corticosteroid therapy supported SLR, which was subsequently confirmed histologically by noncaseating granulomas without viable tumour at surgery. This case highlights pleural involvement in SLR as a rare and diagnostically challenging immune-related adverse event.