Effects of pegfilgrastim on normal biodistribution of ¹⁸F-FDG: Preclinical and clinical studies

The purpose of this study was to evaluate the effects of pegfilgrastim, a long-acting granulocyte colony-stimulating factor, on the normal biodistribution of ¹⁸F-FDG in an animal model and in humans. Methods: Two groups of 12 rats received a single subcutaneous injection of either normal saline or pegfilgrastim. One, 7, 14, and 21 d after injection, biodistribution studies were performed 1 h after ¹⁸F-FDG injection. Sixteen breast cancer patients underwent baseline ¹⁸F-FDG PET/CT and, approximately 1 wk after receiving 1 dose of docetaxel and adjunctive pegfilgrastim, follow-up ¹⁸F-FDG PET/CT (scan 2). Standardized uptake values corrected for lean body mass (SUL) were determined for several normal organs before and after therapy. Results: In rats, bone marrow ¹⁸F-FDG uptake (standardized uptake value) was higher in the pegfilgrastim group 1 d after injection (mean ± SD, 8.3 ± 4.1 vs. 2.5 ± 0.2, P < 0.05), whereas ¹⁸F-FDG uptake in blood was lower (0.41 = 0.06 vs. 0.49 ± 0.01, P < 0.05). In patients, mean SUL was higher in bone marrow (4.49 ± 1.50 vs. 1.33 ± 0.22, P < 0.0001), spleen (3.29 ± 0.83 vs. 1.23 ± 0.23, P < 0.0001), and liver (1.45 ±0.25 vs. 1.31 ± 0.23, P = 0.01) but lower in brain (4.18 ± 0.76 vs. 5.14 ± 1.44, P < 0.01) on scan 2 than on the baseline scan. Conclusion: In both the animal model and humans, pegfilgrastim markedly increased bone marrow uptake of ¹⁸F-FDG and reduced ¹⁸F-FDG uptake in some normal tissues. These profound altera-tions in ¹⁸F-FDG biodistribution induced by pegfilgrastim must be considered when one is evaluating quantitative ¹⁸F-FDG PET scans for tumor response to therapy.