Pirtobrutinib, a non-covalent Bruton tyrosine kinase (BTK) inhibitor, has demonstrated significant potential as an initial therapy for patients with chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL). In a landmark phase III clinical trial, pirtobrutinib met its primary endpoint of non-inferiority regarding overall response rate when compared to ibrutinib, a widely used covalent BTK inhibitor. This trial marks the first direct comparison between a non-covalent and a covalent BTK inhibitor in this patient population.
The study, which took place in Orlando on December 7, 2025, involved 662 adult patients diagnosed with CLL or SLL. Of these participants, 225 had not previously received any treatment, while 437 had either relapsed or were refractory to earlier therapies excluding BTK inhibitors. Participants were randomly assigned to receive either pirtobrutinib or ibrutinib, continuing the assigned treatment until disease progression or unacceptable side effects occurred.
Lead study author Jennifer Woyach, MD, along with colleagues from The Ohio State University College of Medicine, noted, “Pirtobrutinib was clearly non-inferior to ibrutinib, and the response rate actually favors pirtobrutinib in the total cohort.” The overall response rate for those receiving pirtobrutinib was 87.0%, compared to 78.6% for those on ibrutinib. The findings consistently favored pirtobrutinib across various subgroups, including treatment-naive and relapsed/refractory patients.
Study Findings and Implications
The study’s secondary endpoint, progression-free survival (PFS), is still under evaluation, but preliminary results indicate that pirtobrutinib may show advantages here as well. Early data suggest an 18-month PFS rate of 86.9% for pirtobrutinib, compared to 82.3% for ibrutinib. Dr. Woyach remarked, “The PFS is still a little bit immature at this point, but trends toward favoring pirtobrutinib in all of the groups.”
Both treatment arms exhibited similar rates of adverse events (AEs) and treatment discontinuation due to AEs. However, patients receiving pirtobrutinib experienced lower instances of AE-related dose reductions and treatment discontinuation stemming from disease progression. Additionally, cardiovascular AEs such as hypertension and atrial fibrillation appeared less frequently in the pirtobrutinib cohort. These findings suggest that pirtobrutinib may be particularly beneficial for older or more vulnerable patients.
Dr. Woyach emphasized the significance of these results, stating, “While the efficacy and safety of pirtobrutinib have been very clearly established when given after a covalent BTK inhibitor, there are likely going to be subgroups of patients where pirtobrutinib is a more attractive option instead of the covalent BTK inhibitors.”
Future Directions in Treatment
The study was funded by Eli Lilly and Company, the manufacturer of pirtobrutinib, and results were published in the Journal of Clinical Oncology. Dr. Woyach plans to present these findings during a session at the Orange County Convention Center on December 7, 2025.
Researchers will continue to monitor outcomes from this pivotal study and explore further applications of pirtobrutinib, both as a standalone treatment and in combination with other therapies. Investigations into the mechanisms of resistance to non-covalent BTK inhibitors will also inform future treatment strategies.
As the landscape of treatment for CLL and SLL evolves, pirtobrutinib may represent a significant advancement, offering renewed hope for patients and healthcare providers alike.
