Resistance to BTK inhibitors in chronic lymphocytic leukaemia – from the C481S mutation to non-genetic mechanisms of tumour adaptation
Authors:
M. Šimkovič; D. Écsiová
Authors‘ workplace:
IV. interní hematologická klinika, FN Hradec Králové
Published in:
Transfuze Hematol. dnes,32, 2026, No. 2, p. 89-97.
Category:
Review/Educational Papers
doi:
https://doi.org/10.48095/cctahd202615
Overview
Resistance to Bruton tyrosine kinase inhibitors (BTKi) remains a major challenge in the treatment of chronic lymphocytic leukaemia (CLL). This article reviews what is currently known about the genetic and non-genetic mechanisms of resistance. It also presents three clinical case reports. Early research identified the BTK C481S mutation as the primary driver of resistance to covalent BTKi, but newer findings reveal a more complex, evolving picture. Genomic studies over time show that the C481S mutation can appear months before the disease progression. Still, focusing only on this mutation does not explain many relapses. Each generation of BTKi results in distinct mutation patterns. Noncovalent inhibitors like pirtobrutinib create new pressures, leading to kinase-dead BTK variants that continue signalling through other pathways. Many cases of disease progression, especially in patients receiving initial treatment, happen without BTK or PLCG2 mutations. This shows that non-genetic adaptation plays an important role. Changes in pathways like FoxO1-driven transcription and PI3K/AKT or mTORC2 signalling help the cancer survive without BTK. These pathways may be common sites of resistance to different BTKi drugs. Taken together, these findings suggest that we should look beyond just mutations and consider a broader view of resistance. They also raise important questions about the optimal treatment order.
Keywords:
resistance – ibrutinib – chronic lymphocytic leukaemia – acalabrutinib – BTK inhibitors – C481S – non-genetic adaptation – zanubrutinib – pirtobrutinib
Sources
1. Špaček M, Šimkovič M, Pospíšilová Š, et al. Doporučení pro diagnostiku a léčbu chronické lymfocytární leukémie. Transfuze Hematol Dnes. 2025; 31 (3): 205–217. DOI: 10.48095/cctahd2025prolekare.cz15.
2. Šimkovič M, Vejražková E, Écsiová D, Vodárek P. Are we moving toward curative approaches in chronic lymphocytic leukemia? Acta Med. (Hradec Kralove, Czech Repub.). 2025; 68 (4): 113–122. DOI: 10.14712/18059694.2026.1.
3. Košťálová Ľ, Šeda V, Mráz M. Komplexní mechanizmy účinku inhibitorů „BCR signalizace“ a vzniku rezistence na tuto cílenou léčbu u chronické lymfocytární leukemie. Transfuze Hematol Dnes. 2019; 25 (4): 301–308.
4. Byrd JC, Hillmen P, Ghia P, et al. Acalabrutinib versus ibrutinib in previously treated chronic lymphocytic leukemia: results of the first randomized phase III trial. J Clin Oncol. 2021; 39 : 3441–3452. DOI: 10.1200/JCO.21.01210.
5. Brown JR, Eichhorst B, Lamanna N, et al. Sustained benefit of zanubrutinib vs ibrutinib in patients with R/R CLL/SLL: final comparative analysis of ALPINE. Blood. 2024; 144 (26): 2706–2717. DOI: 10.1182/blood.2024024667.
6. Šimkovič M, Écsiová D, Vodárek P. Moderní strategie léčby chronické lymfatické leukémie – význam fixních režimů a jejich opětovného využití. Transfuze Hematol Dnes. 2025; 31 (3): 176–179. DOI: 10.48095/cctahd2025prolekare.cz19.
7. Al-Sawaf O, Robrecht S, Zhang C, et al. Venetoclax-obinutuzumab for previously untreated chronic lymphocytic leukemia: 6-year results of the randomized phase 3 CLL14 study. Blood. 2024; 144 (18): 1924–1935. DOI: 10.1182/blood.2024024631.
8. Eichhorst B, Niemann CU, Kater AP, et al. First-line venetoclax combinations in chronic lymphocytic leukemia. N Engl J Med. 2023; 388 (19): 1739–1754. DOI: 10.1056/NEJMoa221 3093.
9. Brown JR, Seymour JF, Jurczak W, et al. Fixed-duration acalabrutinib combinations in untreated chronic lymphocytic leukemia. N Engl J Med. 2025; 392 (8): 748–762. DOI: 10.1056/NEJMoa2409804.
10. Munir T, Girvan S, Cairns DA, et al. Measurable residual disease–guided therapy for chronic lymphocytic leukemia. N Engl J Med. 2025; 393 : 1177–1190. DOI: 10.1056/NEJMoa 2504341.
11. Al-Sawaf O, Stumpf J, Zhang C, et al. Fixed-duration versus continuous treatment for chronic lymphocytic leukemia. N Engl J Med. 2026; 396 : 1084–1096. DOI: 10.1056/NEJMoa25 15458.
12. Dong X, Tang S, Chen M, et al. Mechanisms of resistance to Bruton’s tyrosine kinase inhibitors: synergistic effects of tumor microenvironment regulation and signaling pathways. Ann Hematol. 2026; 105 (4): 132. DOI: 10.1007/s00277-026-06775-x.
13. Woyach JA, Ruppert AS, Guinn D, et al. BTK C481S-mediated resistance to ibrutinib in chronic lymphocytic leukemia. J Clin Oncol. 2017; 35 : 1437–1443. DOI: 10.1200/JCO.2016. 70.2282.
14. Hamasy A, Wang Q, Blomberg KEM, et al. Substitution scanning identifies a novel, catalytically active ibrutinib-resistant BTK cysteine 481 to threonine (C481T) variant. Leukemia. 2017; 31 (1): 177–185. DOI: 10.1038/leu.2016.153.
15. Bödör C, Kotmayer L, László T, et al. Screening and monitoring of the BTK C481S mutation in a real-world cohort of patients with relapsed/refractory chronic lymphocytic leukaemia during ibrutinib therapy. Br J Haematol. 2021; 194 (2): 355–364. DOI: 10.1111/bjh.17502.
16. Woyach JA, Ghia P, Byrd JC, et al. B-cell receptor pathway mutations are infrequent in patients with chronic lymphocytic leukemia on continuous ibrutinib therapy. Clin Cancer Res. 2023; 29 (16): 3065–3073. DOI: 10.1158/1078-0432.CCR-22-3887.
17. Medina-Gil D, Palomo L, Navarro V, et al. Bruton tyrosine kinase covalent inhibition shapes the immune microenvironment in chronic lymphocytic leukemia. Haematologica. 2025; 110 (8): 1758–1773. DOI: 10.3324/haematol.2024. 286663.
18. Woyach JA, Furman RR, Liu T-M, et al. Resistance mechanisms for the Bruton’s tyrosine kinase inhibitor ibrutinib. N Engl J Med. 2014; 370 (24): 2286–2294. DOI: 10.1056/NEJMoa 1400029.
19. Wang E, Mi X, Thompson MC, et al. Mechanisms of resistance to noncovalent Bruton’s tyrosine kinase inhibitors. N Engl J Med. 2022; 386 (8): 735–743. DOI: 10.1056/NEJMoa 2114110.
20. Kim YJ, Sekiya F, Poulin B, Bae YS, Rhee SG. Mechanism of B-cell receptor-induced phosphorylation and activation of phospholipase C-gamma2. Mol Cell Biol. 2004; 24 (22): 9986–9999. DOI: 10.1128/MCB.24.22.9986-9999.2004.
21. Thangavadivel S, Woyach JA. Genomics of resistance to targeted therapies. Hematol Oncol Clin North Am. 2021; 35 (4): 715–724. DOI: 10.1016/j.hoc.2021.03.004.
22. Blombery P, Chatzikonstantinou T, Gerousi M, et al. Resistance to targeted therapies in chronic lymphocytic leukemia: current status and perspectives for clinical and diagnostic practice. Leukemia. 2025; 39 (9): 2049–2060. DOI: 10.1038/s41375-025-02662-y.
23. Walliser C, Wist M, Hermkes E, et al. Functional characterization of phospholipase C-g2 mutant protein causing both somatic ibrutinib resistance and a germline monogenic autoinflammatory disorder. Oncotarget. 2018; 9 (76): 34357–34378. DOI: 10.18632/oncotarget.26173.
24. Woyach JA, Jones D, Jurczak W, et al. Mutational profile of previously treated chronic lymphocytic leukemia patients progressing on acalabrutinib or ibrutinib. Blood. 2024; 144 (10): 1061–1068. DOI: 10.1182/blood.2023023659.
25. Evans C, Dalal S, Newton D, et al. Acquired Bruton’s tyrosine kinase mutations in patients treated on the ibrutinib and rituximab, ibrutinib alone, and ibrutinib and venetoclax arms of the national multi-centre phase III FLAIR study in previously untreated CLL patients. Blood. 2025; 146 (Suppl 1): 796. DOI: 10.1182/blood-2025-796.
26. Qi J, Endres S, Yosifov DY, et al. Acquired BTK mutations associated with resistance to noncovalent BTK inhibitors. Blood Adv. 2023; 7 (19): 5698–5702. DOI: 10.1182/bloodadvances.2022008955.
27. Tam CS, Balendran S, Blombery P. Novel mechanisms of resistance in CLL: variant BTK mutations in second-generation and noncovalent BTK inhibitors. Blood. 2025; 145 (10): 1005–1009. DOI: 10.1182/blood.2024026672.
28. Brown JR, Li J, Eichhorst BF, et al. Acquired mutations in patients with relapsed/refractory CLL who progressed in the ALPINE study. Blood Adv. 2025; 9 (8): 1918–1926. DOI: 10.1182/bloodadvances.2024014206.
29. Mato AR, Woyach JA, Brown JR, et al. Pirtobrutinib after a covalent BTK inhibitor in chronic lymphocytic leukemia. N Engl J Med. 2023; 389 (1): 33–44. DOI: 10.1056/NEJMoa 2300696.
30. Arthur R, Wathen A, Lemm EA, et al. BTK-independent regulation of calcium signalling downstream of the B-cell receptor in malignant B-cells. Cellular Signalling. 2022; 96 : 110358. DOI 10.1016/j.cellsig.2022.110358.
31. Jain N, Croner LJ, Allan JN, et al. Absence of BTK, BCL2, and PLCG2 mutations in chronic lymphocytic leukemia relapsing after first-line treatment with fixed-duration ibrutinib plus venetoclax. Clin Cancer Res. 2024; 30 (3): 498–505. DOI: 10.1158/1078-0432.CCR-22-3934.
32. Sharman JP, Munir T, Grosicki S, et al. Phase III trial of pirtobrutinib versus idelalisib/rituximab or bendamustine/rituximab in covalent Bruton tyrosine kinase inhibitor-pretreated chronic lymphocytic leukemia/small lymphocytic lymphoma (BRUIN CLL-321). J Clin Oncol. 2025; 43 (22): 2538–2549. DOI: 10.1200/JCO-25-00166.
33. Naeem A, Utro F, Wang Q, et al. Pirtobrutinib targets BTK C481S in ibrutinib-resistant CLL but second-site BTK mutations lead to resistance. Blood Adv. 2023; 7 (9): 1929–1943. DOI: 10.1182/bloodadvances.2022008447.
34. Montoya S, Bourcier J, Noviski M, et al. Kinase-impaired BTK mutations are susceptible to clinical-stage BTK and IKZF1/3 degrader NX-2127. Science. 2024; 383 (6682): eadi5798. DOI: 10.1126/science.adi5798.
35. Casan JML, Seymour JF. Degraders upgraded: the rise of PROTACs in hematological malignancies. Blood. 2024; 143 (13): 1218–1230. DOI: 10.1182/blood.2023022993.
36. Wong RL, Choi MY, Wang H-Y, Kipps TJ. Mutation in Bruton tyrosine kinase (BTK) A428D confers resistance to BTK-degrader therapy in chronic lymphocytic leukemia. Leukemia. 2024; 38 (8): 1818–1821. DOI: 10.1038/s4137 5-024-02317-4.
37. Seda V, Vojackova E, Ondrisova L, et al. FoxO1-GAB1 axis regulates homing capacity and tonic AKT activity in chronic lymphocytic leukemia. Blood. 2021; 138 (9): 758–772. DOI: 10.1182/blood.2020008101.
38. Ondrisova L, Seda V, Hlavac K, et al. FoxO1/Rictor axis induces a non-genetic adaptation to ibrutinib via Akt activation in chronic lymphocytic leukemia. J Clin Invest. 2024; 134 (23): e173770. DOI: 10.1172/JCI173770.
39. Kong C, Wu M, Lu Q, Ke B, Xie J, Li A. PI3K/AKT confers intrinsic and acquired resistance to pirtobrutinib in chronic lymphocytic leukemia. Leuk Res. 2024; 144 : 107548. DOI: 10.1016/j.leukres.2024.107548.
40. Wierda WG, Jacobs R, Barr PM, et al. Consistently high 5.5-year progression-free survival (PFS) rates in patients with and without bulky baseline lymphadenopathy ≥5 cm are associated with high undetectable minimal residual disease (uMRD4) rates after first-line treatment with fixed-duration ibrutinib + venetoclax for chronic lymphocytic leukemia (CLL) /small lymphocytic lymphoma (SLL) in the phase 2 CAPTIVATE study. Blood. 2024; 144 (Suppl 1): 1869. DOI 10.1182/blood-2024-200936.
Labels
Haematology Internal medicine Clinical oncologyArticle was published in
Transfusion and Haematology Today
2026 Issue 2
Most read in this issue
- Thrombotic microangiopathy in the maternity ward from the anaesthesiologist‘s perspective – a case study
- Implementation of the SoHO Regulation and the Management of the Plasma Collection System in the Czech Republic – discussion and position of an interdisciplinary panel
- Development of the epidemiological situation of Hodgkin’s lymphoma in the Czech Republic in the period 2000–2019
- The change of prognosis of 1,492 nonselected patients with multiple myeloma during 60 years in the Middle and partially in the North Moravia region