一位在肺部淋巴發現轉移性黏液土皮樣錯的女性病人，在經過所有傳統診斷工具的檢查後，並未能查出�、發腫瘤。因此病人進一步接受了氣-18-去氧葡萄糖正子攝影全身掃描。結果除了在右頸、右縱煽腔和右肺的高度代謝性的病社外，在左上腹出見了改烈的局部攝取，並被認為是原發的惡性病位。不過最後病理的檢查確定是直腸的良性管狀絨毛性腺擋，而原發部位仍然不明。

A female patient with metastatic mucoepidermoid carcinoma found in pulmonary lymphatics received 18F-FDG positron emission tomography (PET) for detection of unknown primary tumor after unsuccessful conventional diagnostic workup. In addition to multiple hypermetabolic lesions in the right neck， right mediastium and right lung， intense focal uptake was identified at left upper quadrant of the abdomen， which was suspected to be the primary site of malignancy. However， the pathology revealed benign tubovillous adenoma of the colon. The primary tumor has yet to be detected. In this case， FDG PET failed to identify the primary tumor.