A Study to Investigate the Sequencing Strategy of Pirtobrutinib After Disease Progression on First-line Acalabrutinib Treatment for Adult Participants With Chronic Lymphocytic Leukemia or Small Lymphocytic Lymphoma

The purpose of this study is to assess the efficacy and safety of pirtobrutinib in participants with CLL/SLL who have progressed on first-line treatment with acalabrutinib. A subset of participants who have disease progression on pirtobrutinib will be retreated with acalabrutinib to assess whether relapsed CLL can be re-sensitized to a covalent irreversible BTK inhibitor such as acalabrutinib, and thereby, remain on treatment within the BTK inhibitor class rather than transition into another CLL/SLL treatment.

* The study duration for each participant will be up to 3 years in total. * For participants who receive pirtobrutinib alone, the visit frequency will be approximately every month for the first 6 months. After that, the visit frequency will be reduced to one visit approximately every 3 months for the subsequent 12 months. The final part of the Treatment Phase has 2 visits in the space of 6 months. There is one visit to the site after the Treatment Phase. * Participants who have disease progression on pirtobrutinib and go on to receive acalabrutinib retreatment will visit the site approximately once every month for the first 6 months. After that, the visit frequency will be reduced to 2 visits in the space of 6 months. There is one visit to the site after the Treatment Phase.