Flare response versus disease progression in patients with non-small cell lung cancer.

We present a case report of a patient with metastatic non-small cell lung cancer (NSCLC) who had a series of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) scans for assessment of response to treatment. A restaging 18F-FDG PET/CT scan after six cycles showed increased FDG activity in the bone lesions with reduced activity in the lung and liver lesions. The increased bone activity was considered to be due to flare phenomenon rather than metastasis. A short interval follow up scan after 1 month was advised to confirm this interpretation but this repeat scan showed disease relapse. Although the flare phenomenon does exist, caution should be exercised in attributing increased tracer uptake in the lesions in patients with adenocarcinoma of lung and especially those who have received erlotinib during the course of their treatment. Distinguishing the 'flare phenomenon' and 'disease progression' is at times difficult but is important since misdiagnosis may result in an unnecessary delay in patient management.