A Study of NX-5948 in Adults With CLL/SLL Previously Treated With a Bruton's Tyrosine Kinase Inhibitor and a B-cell Lymphoma-2 Inhibitor (DAYBreak CLL-201)

Inclusion Criteria:

* Age: ≥ 18 years
* Confirmed relapsed/refractory CLL/SLL that meets iwCLL criteria for diagnosis and systemic treatment
* Eastern Cooperative Oncology Group (ECOG) performance status of 0-2
* Must have received a covalent BTK inhibitor (BTKi), a non-covalent BTKi, and a BCL-2 inhibitor either in separate lines of therapy or in combination; a line of therapy is considered 2 or more consecutive cycles of a systemic anti-CLL/SLL regimen
* Participants with SLL must have measurable disease by radiographic assessment
* Adequate organ and bone marrow function
* Must sign an informed consent form indicating that he or she understands the purpose of the procedures required for the study and is willing to participate

Exclusion Criteria:

* Known or suspected prolymphocytic leukemia or Richter's transformation before entering study
* Investigational agent or anticancer therapy within 5 half-lives or 14 days (whichever is shorter) before planned start of study drug

  * Antibody therapy must stop at least 4 weeks before the first dose of study drug
  * No other systemic anticancer therapy is allowed at the same time as this study; exception: continuation of hormonal therapy for breast and prostate cancer is allowed, if they are not on the list of prohibited concomitant medications in this study
* Palliative limited-field radiotherapy within 7 days of the first dose of study or broad field radiotherapy within 28 days of first dose of study drug
* Use of systemic corticosteroids \>20 mg/day prednisone or equivalent within the 7 days before start of study drug except for those used as premedication for radio diagnostic contrast
* Use of systemic immunosuppressive drugs other than systemic corticosteroids within 60 days before the first dose of study drug
* Previously treated with a BTK degrader
* Previous chimeric antigen receptor (CAR) T-cell therapy or allogeneic or autologous hematopoietic cell transplant within the past 90 days prior to enrollment
* Thromboembolic events (eg, deep vein thrombosis, pulmonary embolism, or symptomatic cerebrovascular events), stroke, or intracranial hemorrhage within 6 months of planned start of study drug

Note: Other Inclusion/Exclusion criteria may apply as defined in the protocol.