[Suspected radiologic tumor progression in metastatic squamous cell carcinoma with an unexpected etiology]

A 77-year-old man was admitted due to radiologic suspicion of right hilar tumor progression and newly developed right-sided pleural effusion. He had known NSCLC of the left lower lobe (keratinizing squamous cell carcinoma), initially staged T4N1M1c (contralateral lesion and hepatic metastasis), stage IVb. Comorbidities included COPD II, peripheral arterial disease, coronary artery disease, hypertension, and type 2 diabetes. Current oncologic therapy consisted of carboplatin, paclitaxel, and pembrolizumab.The patient presented with exertional dyspnea and reduced breath sounds with dullness to percussion at the right lung base. Bronchoscopic re-biopsy (EBUS-TBNA and transbronchial biopsy) was performed. Pleural cytology was negative for malignancy; therefore, thoracoscopy was conducted, revealing chronic pleuritis without malignant involvement.

Histology showed no metastatic disease but demonstrated diffuse alveolar damage (DAD), consistent with immune-related pneumonitis. A pronounced sarcoid-like granulomatous reaction was observed, also involving the pleura.

Immune-related pneumonitis and pleuritis under PD-1 inhibitor therapy.

Immune-related pneumonitis occurs in approximately 1-5% of patients receiving immune checkpoint inhibitors. Imaging often shows bilateral ground-glass opacities. Histologically, organizing pneumonia is most common; DAD is less frequent. Diagnosis is made by excluding infection and tumor progression.Pleural effusion in oncologic patients is usually interpreted as tumor progression. Immune-mediated pleural involvement is rare and reported only in isolated cases. PD-1 blockade enhances T-cell activation and IFN-γ release, which may promote granuloma formation.Treatment consists of systemic glucocorticoids.