Outpatient Treatment-Related Toxicity after Hospital Discharge among Patients Receiving Lifileucel for Advanced Melanoma.

9557 Background: While inpatient toxicity associated with tumor infiltrating lymphocyte (TIL) therapy and IL-2 administration is well characterized, risks facing patients after hospital discharge are less understood. Better characterization of outpatient adverse effects (AEs) could guide the optimal frequency and duration of follow up for this growing patient population. Methods: We conducted a retrospective analysis of all patients with advanced melanoma discharged from Memorial Sloan Kettering Cancer Center after receiving investigational or commercial lifileucel from October 2020 to October 2024. We reviewed incidence and timing of new Grade 3+ treatment-related AEs (TRAEs), blood product administration, and readmission among all patients from the time of hospital discharge to the time of the start of a subsequent systemic therapy or death. Results: Fifty-three patients successfully discharged after lifileucel administration were identified; patient demographics are included in Table 1 . The median follow up time from discharge in survivors was 5 months (interquartile range (IQR): 3, 18). Two patients (4%) developed new Grade 3+ TRAEs following hospital discharge, including new Grade 3 neutropenia 73 days after discharge and new Grade 3 hypoxia 104 days from discharge. Hypoxia was secondary to pleural effusions that developed in the setting of renal thrombotic microangiopathy. Four patients (7.5%) were readmitted for TRAEs including cytopenias, dyspnea, and syncope while 7 patients (13%) were readmitted for melanoma progression. Readmissions occurred a median of 85 (IQR: 39, 128) days after lifileucel infusion and 69 days (IQR: 19, 98) after initial discharge. Twelve patients (23%) received at least one outpatient blood product transfusion, including packed red blood cells (PRBCs; 10 patients) and platelets (6 patients). Within 30 days of initial discharge, six patients (11%) received at least one PRBC transfusion and 3 patients (5.7%) received at least one platelet transfusion. The median number of transfused PRBC units was 2 (IQR: 1,4) and the median number of platelet transfusions was 4 (IQR: 2, 4). Conclusions: Rates of new severe toxicity and treatment-related readmissions were low among patients discharged post-lifileucel. About one in four patients required blood products after discharge. Identification of risk factors for the development of outpatient TRAEs may inform personalized care following lifileucel administration. Patient demographics. Characteristic N = 53 1 Age at TIL infusion 61 (42, 66) Sex Male 29 (55%) Female 24 (45%) Melanoma subtype Cutaneous 19 (36%) Uveal 9 (17%) Acral 8 (15%) Unknown primary 8 (15%) Mucosal 5 (9.4%) Other 4 (7.5%) BRAF status Mutated 13/51 (25%) Wild type 38/51 (75%) Treatment setting Investigational 45 (85%) Standard of care 8 (15%) 1. N (%); Median (interquartile range).