BTK and B-cell chronic lymphocytic leukemia: In this context, an unaddressed issue remains the responsiveness of the proliferative compartment to newer-generation BTK inhibitors, which provide better and longer remissions; of note, a single CLL patient (TS208) with high PF at progression, treated with pirtobrutinib for over a year, showed a rapid and stable loss of the PF (FP and AZ, personal observation).