(18)F-FDG-PET/CT findings of granulocyte colony stimulating factor (G-CSF)-producing lung tumors.

Tumors producing granulocyte colony stimulating factor (G-CSF), malignant lung tumors in most cases, are rare, and patients present with abnormal elevations of the white blood cell (WBC) count in the absence of any infectious disease. We present the (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG-PET/CT) imaging findings of two cases of G-CSF-producing tumor. PET-CT showed abnormally high uptake of (18)F-FDG not only by the tumor itself but also diffusely throughout the bone marrow. Following resection of the tumor, the blood G-CSF level as well as the WBC count dropped down to normal range in both cases. Histopathological examination of the resected tumor specimens revealed the presence of an enormous number of inflammatory cells within the tumors and positive immunostaining of the tumor cells for G-CSF. The (18)F-FDG-PET/CT findings could be explained by the elevated bone marrow metabolism associated with the excessively active production of granulocytes under G-CSF stimulation, and the (18)F-FDG uptake by the inflammatory cells also contributing to the total tumor uptake of (18)F-FDG. These characteristic imaging findings are expected to be useful for the diagnosis of G-CSF-producing tumors.