The purpose of this study is to learn about the safety of BESPONSA for pediatric patients. .

BESPONSA is approved for treatment of relapsed or refractory CD22-positive acute lymphocytic leukemia for pediatric patients. A type of leukemia (blood cancer) that comes on quickly and is fast growing. In acute lymphocytic leukemia, there are too many lymphoblasts (early-stage white blood cells) in the blood and bone marrow. Also called ALL.

The registration criteria for this study are:

• Never used BESPONSA before
• <18 years at the start of treatment with BESPONSA

All patients in this study will receive BESPONSA according to the prescriptions.

Patients will be followed up as follow

• Treatment phase: From the day of treatment initiation (Day 1) to Day 28 post-treatment to collect information on safety (e.g., adverse events).
• Follow-up phase: From Day 29 post-treatment to Week 52 to collect information on VOD/SOS.

Inclusion Criteria:

1. Patients with relapsed or refractory CD22-positive ALL
2. Patients who have never used BESPONSA before
3. Patients aged <18 years at the start of treatment with BESPONSA

Exclusion Criteria:

• None

Pediatric patients with relapsed or refractory CD22-positive ALL receiving BESPONSA

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.