False negative cases of F-18 fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging in small lung cancer less than 3 cm in size

A considerable number of false negative cases in FDG-PET were seen in small-cell lung cancer, despite the usefulness of this imaging modality. We investigated the correlation between FDG-PET results and the clinicopathological findings in small lung cancers less than 3 cm in size. Fifty-one consecutive cases of surgically resected small lung cancers scanned preoperatively by FDG-PET was assessed. The medical records of each case were reviewed for the maximum tumor size in the CT findings, histology, grade of differentiation, lymphatic and vascular invasion, pleural invasion, lymph node stage, serum level of carcinoembryonic antigen (CEA), and CT findings. All of the 5 cases (4 adenocarcinomas, 1 small-cell carcinoma) less than 1 cm in size were false negatives. In the 46 cases 1-3 cm in size (34 adenocarcinomas, 9 squamous sell carcinomas, 2 large sell carcinomas, 1 small cell carcinoma), false negative results were seen in 8 of 15 cases of well-differentiated adenocarcinoma (53%). In the 8 false negative cases, 1 (13%) lymphatic vessel invasion (ly), 0 (0%) vascular vessel invasion (v), 0 (0%) pleural invasion (p), 0 (0%) lymph node metastasis, 0 (0%) high serum level of CEA, and 5 (63%) cases showing ground-glass opacity on CT were observed. There were significant differences in the factors ly, v, CEA, and CT findings between the 8 false-negative cases and the 26 true positive cases with adenocarcinoma (p < 0.01-0.05). Lung cancers < 1 cm in size cannot be detected in FDG-PET. Adenocarcinomas of the lung 1-3 cm in size with false negatives in FDG-PET showed significantly less invasiveness than the true positives.