A Case of FDG-PET Positive Lung Cancer With Hilar Lymph Node Metastases, Which Showed False Negative FDG-PET Findings

Background. The accurate evaluation of cancer metastases to hilar or mediastinal lymph nodes or distant organs is very important for the decision of treatment strategy in lung cancer. Recently, positron emission tomography with 18F-fluoro-2-deoxy-D-glucose (FDG-PET) has become considered useful for the staging of lung cancers. Case. A 55-year-old man with an adenocarcinoma of the right lung was admitted to our hospital for surgical treatment. Enhanced CT scan showed a tumor (measuring 70 mm in diameter) in S9 and swollen hilar lymph nodes (#11s and #11i) and left adrenal gland. FDG-PET showed positive accumulation at the primary site, but not in the hilar lymph nodes and the left adrenal gland. Right lower lobectomy was planned based on a pre-operative diagnosis as clinical stage IB (cT2N0M0). Since intraoperative frozen sections of the hilar lymph nodes showed metastases of mucinous adenocarcinoma, right middle and lower lobectomy with lymphadenectomy was performed. Histologically, the right lung tumor was adenocarcinoma with mixed subtypes, consisting of colloid adenocarcinoma and solid adenocarcinoma with mucin. Metastatic lymph nodes showed features of colloid adenocarcinoma with abundant mucin. Conclusion. The analysis of FDG-PET false positive cases and negative cases of lung cancers should improve the accuracy of lung cancer staging.