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

Using PET, we investigated the change in F-18-fluorordeoxyglucose (FDG) upt ake in the spleen after granulocyte colony-stimulating factor (G-CSF) treat ment. Methods: Forty-two FDG PET scans in 12 patients with locally advanced breast cancer who received G-CSF treatment were studied (12 baseline, 10 d uring G-CSF, 20 after G-CSF treatment). The PET images obtained at 50-60 an d 60-70 min after intravenous FDG (370 MBq) injection were assessed visuall y and were compared with those before G-CSF treatment. For a semiquantitati ve index of FDG uptake, we determined the standardized uptake value calcula ted 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 FD G uptake (3 slightly, 6 substantially). After G-CSF treatment (n = 20), 13 (65%) showed no change, 7 (35%) showed slightly increased uptake, but no ca se showed substantially increased FDG uptake in the spleen (P = 0.0003). Ou t of 30 PET scans obtained during and after G-CSF treatment, 16 (53%) showe d increased FDG uptake in the spleen (10 slightly, 6 substantially), wherea s 26 (87%) showed increased bone marrow FDG uptake (14 slightly, 12 substan tially). The FDG uptake in other normal organs (liver, blood and lung) show ed 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 tr eatment (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). Ther e was a significant correlation between the SUL ratios in the spleen and th ose in the bone marrow (r = 0.778, P < 0.0001), whereas there were no corre lations between those in other organs and those in the bone marrow. Conclus ion: Substantially increased FDG uptake was observed in the spleen during a nd 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 unde rstanding of this phenomenon will be increasingly important when interpreti ng FDG PET images in cancer patients to avoid confusing this normal phenome non with pathological splenic (tumor) involvement.