Pirtobrutinib at the Crossroads: Shaping Its Future Role in Chronic Lymphocytic Leukemia ( <scp>CLL</scp> ) Care

Covalent Bruton tyrosine kinase inhibitor (cBTKi)-based regimens have redefined therapy for chronic lymphocytic leukemia (CLL). However, continuous treatment with BTKis can select for therapy resistance, typically associated with BTK C481 mutations and fosfolipasi C gamma 2 (PLCγ2) activation. In addition, continuous BTKi therapy poses challenges for treatment interruptions and dose modifications, with implications for clinical outcomes. Pirtobrutinib, a highly selective, reversible (noncovalent) BTKi, inhibits BTK independently of C481 and maintains sustained target engagement. In patients with cBTKi-pretreated relapsed/refractory (R/R) CLL, the BRUIN-CLL-321 trial demonstrated improved progression-free survival (PFS) and time to next treatment (TTNT) compared with idelalisib/rituximab or bendamustine/rituximab, accompanied by a favorable tolerability profile. Data from randomized phase III BRUIN-CLL-313 and BRUIN-CLL-314 trials demonstrate the superiority of pirtobrutinib over chemoimmunotherapy in untreated patients and non-inferiority to ibrutinib in untreated patients or in patients with R/R disease who had no prior exposure to cBTKis. These data are not sufficient to justify a change in clinical practice; however, they lay the groundwork for a potential future repositioning of pirtobrutinib from the treatment of R/R CLL to earlier lines of therapy. In this review, we address a range of current and prospective aspects of pirtobrutinib-based therapies: (1) the strengths and limitations of the trial datasets; (2) the biological rationale for frontline noncovalent BTK inhibition; (3) sequencing trade-offs; and (4) prospective scenarios, including combination strategies and time-limited regimens.