Trial: Long-term observational follow-up of patients previously treated with CAR T cells (from Phase 1 trials NCT05660369 and NCT06026319), no new therapy is given—only assessments (blood tests, CT/PET-CT, tumor biopsy). Drugs/interventions: Prior CAR T-cell products (autologous, gene‑modified cellular immunotherapy, gene therapy). Mechanism of action: T cells engineered with a chimeric antigen receptor that confers antibody-like recognition of a tumor antigen and activates T-cell effector functions via CD3ζ and a costimulatory domain (e.g., CD28 or 4‑1BB), leading to cytotoxic killing, cytokine release, expansion, and persistence. Targets: Malignant cells expressing the CAR antigen (antigen varies by parent trials). Pathways: CAR/TCR signaling and downstream immune/cytokine activation. Purpose: monitor delayed AEs and durability of response.