3022 Background: Molecular imaging with FDG-PET/CT (PET/CT) is an established modality for response assessment in lymphoma patients (pts) undergoing treatment (Tx). However, pts treated with novel immunotherapies may have false positive PET/CT findings due to tumor site and systemic inflammation. In particular, Tx with CTL019cells(autologous chimeric antigen receptor modified T-cells redirected at CD19) can be complicated by ‘cytokine release syndrome’ (CRS) due to a severe systemic inflammatory reaction. Infiltration of tumors by activated CTL019 cells may impact radiographic and functional imaging findings. The role of PET/CT in pts treated with CTL019has not previously been described. Methods: We performed a pilot, single arm, prospective study to explore the utility of early PET/CT in pts with diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) undergoing Tx with CTL019 T-cells. Pts had PET/CT prior to CTL019infusion and then early PET/CT at 1 month (m) post-Tx. The primary outcome was the amount/change in metabolically active tumor volume (MTV) and FDG uptake. Secondary outcomes included the association of early PET/CT with formal response assessment by 3 m CT scan and the effect of CRS on PET/CT results. Results: We enrolled 6 pts (DLBCL 4; FL 2). 5 of 6 had baseline PET/CT with active disease. 4 of 6 pts developed CRS but all resolved symptoms prior to the 1 m scan. On the 1 m PET/CT, 3 had response (CR or PR) and 3 had disease progression (PD). There was 100% correlation of early PET/CT result with 3 month CT response assessment (Table). Development of CRS did not confound PET/CT findings. Conclusions: In DLBCL and FL pts on Tx with CTL019, early PET/CT may predict response to this novel immunotherapy. The development of CRS did not influence image assessment at 1 m. We plan to include early PET/CT in future CTL019 lymphoma studies to better define its role in this setting.