After Ibrutinib Resistance: CLL/SLL and MCL Next Steps, Progression vs Intolerance

　　1.Progression or Intolerance First

　　Lymph node growth,worsening CBC,or new symptoms under ibrutinib are not automatically resistance.

　　Progression:tumor enlargement on therapy,persistent lymphocyte rise,organ involvement,imaging/biopsy confirming active disease.

　　Intolerance:bleeding,AFib,hypertension,severe diarrhea,infection,transaminitis—disease still controlled.

　　Intolerance may allow another BTK class switch;confirmed progression needs pathway change.

　　2.Why Not Just“Switch BTK Inhibitor”

　　Ibrutinib,acalabrutinib,zanubrutinib are covalent BTK inhibitors sharing C481 binding.

　　Resistance mechanisms:

　　BTK C481S/C481Y mutational escape;

　　PLCG2 gain-of-function bypass;

　　PI3K-AKT/NF-κB bypass;

　　microenvironment protection.

　　If progression occurred on ibrutinib,another covalent BTK often shows cross-resistance;only intolerance-based switching is reasonable.

　　3.CLL/SLL After Ibrutinib

　　Decide by prior lines,remission duration,TP53/del(17p),fitness,prior venetoclax.

　　Options:

　　Venetoclax+anti-CD20​(rituximab/obinutuzumab)—non-BTK pathway.

　　Pirtobrutinib​—non-covalent BTK,useful if BTK-pathway dependence persists.

　　PI3K inhibitor/novel combos​—selected cases.

　　CAR-T or allo-HSCT​—high-risk,Richter transformation,double-class failure.

　　Guideline note:BTK/PLCG2 testing helps confirm mechanism,but mutation alone without progression is not an automatic switch.

　　4.MCL After Ibrutinib

　　Stratify by timing:

　　Late relapse(>24 months off BTK):covalent BTK rechallenge,lenalidomide+rituximab possible.

　　Progression on ibrutinib(<24 months):

　　pirtobrutinib(non-covalent BTK);

　　CAR-T:brexu-cel;

　　CD20×CD3 bispecific after CD20 recheck;

　　clinical trial.

　　Re-biopsy if blastoid/polymorphic morphology,TP53 abnormality,or rapid acceleration.

　　5.Work-up Before Switching

　　CBC,LFT,creatinine;

　　CT/PET-CT;

　　BTK/PLCG2 testing on progression;

　　TP53,del(17p),IGHV for CLL;

　　ECG if AFib history or reuse BTK;

　　drug interactions:CYP3A strong inhibitor/inducer,anticoagulants;

　　adherence check.

　　6.Common Mistakes

　　dose escalation on node growth→more bleeding/AFib,no benefit;

　　assume acalabrutinib will work→covalent cross-resistance;

　　intolerance=resistance→wrong;

　　no symptoms=fine→CLL rich-lymphocyte progression exists.