False-positive findings on [18F]FDG-PET caused by non-neoplastic cellular elements after neoadjuvant chemoradiotherapy for non-small cell lung cancer.

We report two patients with non-small cell lung cancer who had a pathologically complete response after neoadjuvant chemoradiotherapy, although they had positive [(18)F]fluoro-deoxyglucose positron emission tomography ([(18)F]FDG-PET) scans. They underwent concurrent chemoradiotherapy, which resulted in a partial response determined by computed tomography (CT). While [(18)F]FDG-PET after chemoradiotherapy was positive, pathological examination showed that the tumors were fibrotic lesions with infiltration of lymphocytes and macrophages, with the appearance of metaplastic epithelial cells. The reasons for the false-positive results on [(18)F]FDG-PET were considered to be the high uptake of FDG in non-neoplastic inflammatory cellular elements, i.e. macrophages, lymphocytes and metaplastic epithelial cells, and squamous metaplasia induced by chemoradiotherapy. Although several studies demonstrated that [(18)F]FDG-PET could predict the response of neoadjuvant treatment of non-small cell lung cancer, one should bear in mind that false-positive results could be observed in pathological complete response of non-small cell lung cancer after neoadjuvant chemoradiotherapy.