[False positive result of 18F-FDG PET in patient with lung cancer due to sarcoid-like reaction in regional lymph nodes].

The development of non-caseating granulomas in patients with neoplastic diseases is referred to as a sarcoid-like reaction. This reaction may be found in the primary tumour or near it; however, it is commonly seen in the regional lymph nodes, and usually subsides after treatment of the underlying disease. The pathogenesis of this process has not been fully explained. Sarcoid-like reactions occur in 4.4% of solid tumours, 7.3% of patients with non-Hodgkin's lymphoma, and 13.8% of patients with Hodgkin's lymphoma. The radiological image of increased lymph nodes due to the sarcoid-like reaction is similar to that of lymphadenopathy with neoplastic aetiology, and may create diagnostic difficulties. The paper presents the case of a patient with a sarcoid-like reaction in regional lymph nodes caused by lung cancer, and describes difficulties in the interpretation of results from positron emission tomography (18F-FDG PET), which may have led to inappropriate treatment. False-positive accumulation of radiotracer (fluorodeoxyglucose, FDG) in mediastinal and hilar lymph nodes in the patient, who had chemotherapy and right-side pneumonectomy, was unambiguously interpreted by the radiologists as the relapse of lung cancer. Considering the fact that the patient was in a very good condition and presented with no clinical symptoms that indicated the progression of cancer, we extended the medical diagnostics. The performed procedures ruled out neoplastic process and confirmed our assumptions regarding sarcoid-like reaction. Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) was the diagnostic procedure that provided conclusive results. Sarcoid granulomas were identified by the pathomorphologist in the specimen. The patient avoided toxic treatment.