This study investigates treatments for B-cell acute lymphoblastic leukemia (B-ALL) that has returned after improvement, also known as relapsed B-ALL. The purpose is to compare two treatments: a standard combination of chemotherapy and an investigational medication called blinatumomab. B-ALL is a type of cancer affecting white blood cells, and relapsed means the cancer has come back after treatment.

Participants will be randomly assigned to different study arms based on their risk level. The study will compare disease-free survival among high-risk and intermediate-risk patients receiving either additional chemotherapy or blinatumomab. Low-risk patients will receive either chemotherapy alone or chemotherapy with blinatumomab. The study involves different treatment blocks and aims to determine which approach is more effective.

• Who can participate: Participants must have experienced their first relapse of B-cell acute lymphoblastic leukemia. They should not have had prior treatment with the investigational medication; certain conditions, such as Philadelphia chromosome positive leukemia and specific genetic syndromes, are exclusions.
• Study details: Participants will be assigned to receive either chemotherapy or an investigational medication called blinatumomab, depending on their risk classification.