Palbociclib in Combination With Chemotherapy in Pediatric Patients With Relapsed or Refractory Acute Lymphoblastic Leukemia (RELPALL2)

This study (RELPALL2) tests the combination of palbociclib (a drug that pauses cancer cell growth) with chemotherapy in children and young adults (under 25) with acute lymphoblastic leukemia (ALL) — a type of blood cancer — that has returned or stopped responding to prior treatments. **You may be eligible if...** - You are under 25 years old with ALL that has relapsed or is refractory (not responding to treatment) - You have confirmed leukemia blasts in bone marrow or blood - Your general functional status is adequate (Karnofsky/Lansky score >50) - Your heart, liver, kidney, and lung function meet the required thresholds - You have recovered from the effects of prior therapy **You may NOT be eligible if...** - You have isolated CNS or testicular leukemia only (without bone marrow involvement) - You have previously received palbociclib or other CDK4/6 inhibitors without benefit - You have active HIV or active hepatitis B or C - You are pregnant or breastfeeding - You have an active uncontrolled infection - Your cumulative anthracycline dose is already very high (above 400 mg/m²) Talk to your doctor to see if this trial is right for you.