Figure 2.

Axial fusion FDG PET/CT image in a 28-year-old woman with a metastatic neuroendocrine tumor (yellow circle). A pelvic lymph node metastasis demonstrates high FDG uptake (SUV_max, 4.9), and a separately performed ¹¹¹In pentetreotide study demonstrated little or no uptake in this region. These findings are consistent with dedifferentiated tumor. Neuroendocrine tumors can demonstrate the flip-flop phenomenon, in which FDG uptake is inversely correlated with ¹¹¹In pentetreotide uptake. Increasing FDG uptake and decreasing ¹¹¹In pentetreotide uptake correlate with dedifferentiation and poor prognosis.