RT Journal Article SR Electronic T1 Imaging of CTLA4 Blockade–Induced Cell Replication with 18F-FLT PET in Patients with Advanced Melanoma Treated with Tremelimumab JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 340 OP 346 DO 10.2967/jnumed.109.070946 VO 51 IS 3 A1 Antoni Ribas A1 Matthias R. Benz A1 Martin S. Allen-Auerbach A1 Caius Radu A1 Bartosz Chmielowski A1 Elizabeth Seja A1 John L. Williams A1 Jesus Gomez-Navarro A1 Timothy McCarthy A1 Johannes Czernin YR 2010 UL http://jnm.snmjournals.org/content/51/3/340.abstract AB Preclinical models predict that blockade of the coinhibitory molecule cytotoxic T lymphocyte–associated antigen 4 (CTLA4) on lymphocytes results in the release of a cell cycle inhibitory checkpoint, allowing lymphocyte proliferation, tumor targeting, and regression. However, there is a paucity of data demonstrating that lymphocyte proliferation does occur in humans treated with CTLA4-blocking antibodies. Methods: We tested the role of whole-body molecular imaging in patients with advanced melanoma receiving the CTLA4-blocking antibody tremelimumab, allowing the analysis of changes in glucose metabolism using the PET probe 18F-FDG and cell replication with the PET probe 3′-deoxy-3′-18F-fluorothymidine (18F-FLT). Results: PET/CT scans obtained at a median of 2 mo after initial dosing did not demonstrate significant changes in lesion size or 18F-FDG or 18F-FLT uptake when focusing on metastatic lesions. Similarly, there was no difference in 18F-FDG uptake in the non–melanoma-involved spleen. However, there were significant increases in standardized uptake values for 18F-FLT in the spleen using post- and pretremelimumab treatment scans. Conclusion: Molecular imaging with the PET probe 18F-FLT allows mapping and noninvasive imaging of cell proliferation in secondary lymphoid organs after CTLA4 blockade in patients with metastatic melanoma.