This is a global multicenter, open label, randomized, registrational phase III study to investigate the efficacy and safety of lisaftoclax in combination with BTK inhibitors in CLL/SLL patients who previously treated with BTK inhibitors

Approximately 440 patients will be enrolled, the patients who meet the eligibility criteria will be randomized in a 1:1 ratio to investigational arm (lisaftoclax in combination with a BTK inhibitor) or the control arm (BTK inhibitor alone). These patients with CLL/SLL have been on BTKi monotherapy and meet all other protocol required eligibility criteria.

Inclusion Criteria:

1. Age ≥ 18 years.

2. Patients that have documented CLL/SLL who meet iwCLL 2018 criteria for CLL treatment guidelines are eligible for treatment and must be receiving BTKi monotherapy for at least 12 months

3. ECOG Performance Status grade 0-2

4. Adequate bone marrow function independent of growth factor or transfusion support within 2 weeks of screening initiation as follows:

   • Absolute neutrophil count ≥ 1.0 × 109/L
   • Platelet counts ≥ 75 × 109/L; in cases of thrombocytopenia
   • Total hemoglobin ≥ 9 g/dL,

5. Adequate renal function

   • Creatinine clearance must be > 50 ml/min directly measured with 24hr urine collection or calculated according to the modified formula of Cockcroft and Gault (for men: GFR ≈ ((140 - age) x actual body weight)/(72 x creatinine), for women x 0.85) or an equally accurate method.
   • For patients with creatinine values within the normal range, the calculation of clearance is not necessary. Dehydrated patients with an estimated creatinine clearance less than 50 ml/min may be eligible if a repeat estimate after adequate hydration is > 50 ml/min.

6. Adequate liver function as indicated by:

   • Total bilirubin ≤ 1.5 x ULN, except patients with known Gilbert's Syndrome
   • Aspartate aminotransferase (AST) ≤ 2.5 x the institutional ULN value
   • Alanine aminotransferase (ALT) ≤ 2.5 x the institutional ULN value,
   • International normalized Ratio (INR), Prothrombin Time (PT) or Activated Partial Thromboplastin time (APTT) ≤ 1.5×ULN.

7. Ability and willingness to provide written informed consent and to adhere to the study visit schedule and other protocol requirements