Abstract About 70% of patients with large B-cell lymphoma (LBCL) who are treated with axicabtagene ciloleucel (axi-cel) and who achieve a partial response (PR) or stable disease (SD) on the day 30 (D30) positron emission tomography (PET)–computed tomography (CT) scan progress; however, the factors that are predictive of progression are unknown. This a retrospective study of patients with LBCL who were treated with axi-cel at MD Anderson Cancer Center between January of 2018 and February of 2021. Among 50 patients with D30 PR/SD, 13 (26%) converted to a complete response (CR). Among 95 patients with a D30 CR, 72 (76%) remained in CR. On univariate analysis, the only day −5 characteristic associated with conversion from D30 PR/SD to subsequent CR was a higher platelet count (P = .05). The only D30 factor associated with conversion from D30 PR/SD to subsequent CR was a lower maximum standardized uptake volume (SUVmax; P < .001); all patients with D30 SUVmax ≥ 10 progressed. After a median follow-up of 12 months, no significant difference in median progression-free survival was observed between patients who converted from D30 PR/SD to subsequent CR and those who had been in CR since D30 (P = .19). Novel predictive and prognostic markers based on tissue biopsy and noninvasive diagnostic assays are needed to more effectively identify these patients and characterize the biology of their residual disease.