Splenic fluorodeoxyglucose uptake increased by granulocyte colony- stimulating factor therapy: PET imaging results

Using PET, we investigated the change in ¹⁸F-fluorordeoxyglucose (FDG) uptake in the spleen after granulocyte colony-stimulating factor (G-CSF) treatment. Methods: Forty-two FDG PET scans in 12 patients with locally advanced breast cancer who received G-CSF treatment were studied (12 baseline, 10 during G-CSF, 20 after G-CSF treatment). The PET images obtained at 50-60 and 60-70 min after intravenous FDG (370 MBq) injection were assessed visually and were compared with those before G-CSF treatment. For a semiquantitative index of FDG uptake, we determined the standardized uptake value calculated on the basis of predicted lean body mass (SUL) on these images, and we calculated the SUL ratios normalized to their baseline SUL values. Results: During G-CSF treatment (n = 10), 9 scans (90%) showed increased splenic FDG uptake (3 slightly, 6 substantially). After G-CSF treatment (n = 20), 13 (65%) showed no change, 7 (35%) showed slightly increased uptake, but no case showed substantially increased FDG uptake in the spleen (P = 0.0003). Out of 30 PET scans obtained during and after G-CSF treatment, 16 (53%) showed increased FDG uptake in the spleen (10 slightly, 6 substantially), whereas 26 (87%) showed increased bone marrow FDG uptake (14 slightly, 12 substantially). The FDG uptake in other normal organs (liver, blood and lung) showed no change during or after G-CSF treatment. Similar to the change in the bone marrow, the SULs in the spleen significantly increased during G-CSF treatment (baseline, 1.50 ± 0.31, versus during G-CSF, 2.69 ± 0.84; P = 0.0004), then decreased after discontinuation of G-CSF (1.65 ± 0.23). There was a significant correlation between the SUL ratios in the spleen and those in the bone marrow (r = 0.778, P < 0.0001), whereas there were no correlations between those in other organs and those in the bone marrow. Conclusion: Substantially increased FDG uptake was observed in the spleen during and after G-CSF treatment, although this change was less frequent and not as marked as the change observed in the bone marrow. The recognition and understanding of this phenomenon will be increasingly important when interpreting FDG PET images in cancer patients to avoid confusing this normal phenomenon with pathological splenic (tumor) involvement.