The study has 4 parts: screening, taking the study drug, stopping the drug, and follow-up. You’ll get tests like blood work, heart checks, and scans. You’ll be randomly given one of two medicines: BGB-16673 or Pirtobrutinib, both taken once a day. After stopping the medicine, you’ll return for a check-up in about a month. If your cancer hasn’t gotten worse, you’ll visit every 6 months. If it has, the study team will check on you by phone or email. The whole study may last about 3 years with around 13 visits.

Relapsed/Refractory Chronic Lymphocytic Leukemia (CLL) or Small Lymphocytic Lymphoma (SLL)

Who can join the study:

• Adults with a type of blood cancer called CLL or SLL who need treatment.
• They must have had certain treatments before and still have signs of the disease.

Who cannot join the study:

• People with other serious blood cancers or brain problems.
• People who had certain types of transplants or treatments recently.
• People with serious allergies to the study medicine.
• People with infections or bleeding problems.
• People who had a stroke or brain bleeding in the last 6 months.
• People who take certain blood-thinning medicines or have HIV.

Doctors are doing a study to test two new medicines called BGB-16673 and Pirtobrutinib. They want to find out which one works better and is safer for people who have a type of blood cancer called CLL or SLL and have already had treatment before.