NCT06476665 is an observational post‑marketing safety study of BESPONSA (inotuzumab ozogamicin) in pediatric (<18) patients with relapsed/refractory CD22‑positive acute lymphoblastic leukemia in Japan, all participants receive BESPONSA per standard prescription. Drug/intervention: BESPONSA is an antibody‑drug conjugate (humanized anti‑CD22 IgG4 monoclonal antibody) linked to the cytotoxic antibiotic calicheamicin. Mechanism: the antibody binds CD22 on B‑lineage lymphoblasts, is internalized, and releases calicheamicin, which binds the DNA minor groove and induces double‑strand breaks, triggering apoptosis. Cells/pathways targeted: CD22‑expressing B‑cell precursors/lymphoblasts, CD22‑mediated endocytosis, DNA damage and apoptotic signaling pathways. Safety focus includes monitoring for hepatic veno‑occlusive disease/sinusoidal obstruction syndrome (VOD/SOS).