{"entity":{"id":"btk-c481s","kind":"biomarker","name":"BTK resistance mutations: C481S, and L528W and T474I after the non-covalent inhibitors","aka":["BTK C481S","BTK Cys481Ser","BTK L528W","BTK T474I","BTK resistance mutation","ibrutinib resistance mutation"],"tldr":"A change in the enzyme BTK at the exact point where the drug grips it. The enzyme keeps working and the drug no longer holds, which is the usual reason a BTK inhibitor stops working after it has been working well.","summary":"Ibrutinib and its covalent successors bind cysteine 481 of BTK irreversibly. Whole-exome sequencing of paired baseline and relapse samples from six patients with acquired resistance found a cysteine-to-serine substitution at that residue in five of them, and three distinct PLCG2 mutations in two; functional work showed that C481S leaves the protein only reversibly inhibited, and that the PLCG2 changes R665W and L845F are gain-of-function lesions producing autonomous B-cell receptor activity. Neither was found in nine patients with prolonged lymphocytosis who were still responding (Woyach 2014).\n\nThe answer to C481S is a non-covalent inhibitor that does not need the cysteine. Pirtobrutinib produced an overall response of 73.3% in 247 patients who had already received a covalent BTK inhibitor, with median progression-free survival of 19.6 months (Mato 2023). Resistance to that in turn runs through different residues: the kinase-dead L528W substitution was found in 7 of 13 patients progressing on zanubrutinib against 1 of 24 on ibrutinib, and in two patients it was enriched further under pirtobrutinib, which is cross-resistance rather than a new event; both of those patients responded to venetoclax afterwards (Blombery 2022).","asOf":"2026-09-30","links":[{"label":"Woyach et al., N Engl J Med 2014: BTK C481S and PLCG2 resistance mutations under ibrutinib","url":"https://doi.org/10.1056/NEJMoa1400029"},{"label":"Blombery et al., Blood Adv 2022: enrichment of BTK Leu528Trp on zanubrutinib and cross-resistance to pirtobrutinib","url":"https://doi.org/10.1182/bloodadvances.2022008325"},{"label":"Mato et al., N Engl J Med 2023: pirtobrutinib after a covalent BTK inhibitor (BRUIN, 317 patients)","url":"https://doi.org/10.1056/NEJMoa2300696"}],"tags":["biomarker","resistance","lymphoma"],"related":["bcl2-g101v"],"cancers":["mantle-cell-lymphoma","waldenstrom","non-hodgkin-lymphoma","marginal-zone-lymphoma"],"sections":[],"technologies":["cgp","liquid-biopsy"],"targets":["btk","plcg2"],"drugs":["ibrutinib","acalabrutinib","zanubrutinib","pirtobrutinib","venetoclax"],"companies":[],"institutions":[],"pathways":["bcr-signalling","resistance-routes-map"],"terms":["resistance","cross-resistance","ngs"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"target":"btk","measurement":"sequencing-variant","scoringRule":{"text":"Deep targeted sequencing of BTK and PLCG2 on blood or marrow at progression, reported by specific residue rather than as BTK mutated, because the residue decides what works next: C481 substitutions are answered by a non-covalent inhibitor, while L528W and T474I are not. Subclonal variants at low allele fraction can appear months before clinical progression, so the depth of the assay matters.","quote":"We identified a cysteine-to-serine mutation in BTK at the binding site of ibrutinib in five patients and identified three distinct mutations in PLCγ2 in two patients.","source":"https://doi.org/10.1056/NEJMoa1400029","sourceLabel":"Woyach et al., New England Journal of Medicine 2014"},"thresholds":[],"definedBy":{"label":"Woyach et al., N Engl J Med 2014: BTK C481S and PLCG2 resistance mutations under ibrutinib","url":"https://doi.org/10.1056/NEJMoa1400029"},"tests":[],"assays":[],"companionDiagnostics":[],"forPatient":"If a BTK inhibitor has stopped working, this test can say whether a different BTK inhibitor is still worth trying or whether the next treatment needs to work in another way altogether, such as venetoclax, a bispecific antibody or CAR-T. A report that says only BTK mutated has not answered the question; the exact change matters."},"route":"/biomarkers/btk-c481s/","neighbours":{"biomarker":[{"id":"bcl2-g101v","kind":"biomarker","name":"BCL2 G101V and the other venetoclax binding-site mutations","route":"/biomarkers/bcl2-g101v/"}],"cancer":[{"id":"mantle-cell-lymphoma","kind":"cancer","name":"Mantle cell lymphoma","route":"/cancers/mantle-cell-lymphoma/"},{"id":"marginal-zone-lymphoma","kind":"cancer","name":"Marginal zone lymphoma","route":"/cancers/marginal-zone-lymphoma/"},{"id":"non-hodgkin-lymphoma","kind":"cancer","name":"Non-Hodgkin lymphoma (all types)","route":"/cancers/non-hodgkin-lymphoma/"},{"id":"waldenstrom","kind":"cancer","name":"Waldenström macroglobulinaemia","route":"/cancers/waldenstrom/"}],"technology":[{"id":"cgp","kind":"technology","name":"Comprehensive genomic profiling","route":"/technologies/cgp/"},{"id":"liquid-biopsy","kind":"technology","name":"Liquid biopsy (ctDNA)","route":"/technologies/liquid-biopsy/"}],"target":[{"id":"btk","kind":"target","name":"BTK (Bruton tyrosine kinase)","route":"/targets/btk/"},{"id":"plcg2","kind":"target","name":"PLCG2","route":"/targets/plcg2/"}],"drug":[{"id":"acalabrutinib","kind":"drug","name":"Acalabrutinib","route":"/drugs/acalabrutinib/"},{"id":"ibrutinib","kind":"drug","name":"Ibrutinib","route":"/drugs/ibrutinib/"},{"id":"pirtobrutinib","kind":"drug","name":"Pirtobrutinib","route":"/drugs/pirtobrutinib/"},{"id":"venetoclax","kind":"drug","name":"Venetoclax","route":"/drugs/venetoclax/"},{"id":"zanubrutinib","kind":"drug","name":"Zanubrutinib","route":"/drugs/zanubrutinib/"}],"pathway":[{"id":"bcr-signalling","kind":"pathway","name":"B-cell receptor / BTK signalling (to NF-κB)","route":"/pathways/bcr-signalling/"},{"id":"resistance-routes-map","kind":"pathway","name":"Resistance routes: how a blocked pathway comes back","route":"/pathways/resistance-routes-map/"}],"term":[{"id":"cross-resistance","kind":"term","name":"Cross-resistance","route":"/terms/cross-resistance/"},{"id":"resistance","kind":"term","name":"Drug resistance (primary and acquired)","route":"/terms/resistance/"},{"id":"ngs","kind":"term","name":"Next-generation sequencing (NGS)","route":"/terms/ngs/"}]}}