PO_I_L: Pathology and Oncology I. Lectures
Lili Kotmayer1, Csaba Bödör1, Donát Alpár1
1 HCEMM-SE Molecular Oncohematology Research Group, 1st Department of Pathology and Experimental Cancer Research, Semmelweis University, Budapest, Hungary
Introduction: Treatment of relapsed/therapy refractory chronic lymphocytic leukemia (R/R CLL) has been revolutionized by the Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib. Despite the outstanding response rates, a subset of CLL patient receiving ibrutinib experience disease progression with the majority of secondary ibrutinib resistant cases harbouring mutations in BTK and PLCG2 genes. Although longitudinal studies have revealed the significance of early detection of the most common resistance mutation BTK p.C481S, international recommendations for timing and frequency of monitoring for this genetic alteration have not yet been established.
Aims: Our aim was to develop a droplet digital PCR based assay for ultrasensitive detection of the most common BTK resistance mutation p.C481S. We aimed to scrutinize the correlation between disease progression and the emergence of BTK p.C481S and to assess the clinical value of sensitive screening for this mutation.
Methods: Serial peripheral blood samples from 83 R/R CLL patients receiving single-agent ibrutinib for a minimum of 12 months were collected from 11 Hungarian oncohematological centers. Following the assessment of leukemic cell purity by flow cytometry using CD5/CD19 markers, genomic DNA was extracted from peripheral blood mononuclear cells. Fractional abundance of the BTK p.C481S mutation was quantified using custom-designed locus-specific assays on a QX200 droplet digital PCR system (BioRad, USA).
Results: During a median follow-up time of 40 months, BTK p.C481S mutation was detected in 48.2% (40/83) of the patients, with 80% (32/40) of them experiencing disease progression. Emergence of the BTK mutation predated the first clinical signs of relapse with median of 9 months. BTK C481S was detected in 72.7% (32/44) of patients progressing on ibrutinib. Subsequent BCL2 inhibitor venetoclax was administered to patients with BTK p.C481S experiencing disease progression conferring the successful elimination of the mutant subclone ubiquitously across the cases.
Conclusions: In three-quarters of R/R CLL patients with secondary ibrutinib resistance, ultrasensitive time-resolved monitoring of BTK C481S by ddPCR allows for the prediction of an impending relapse, months before the first clinical signs of disease progression.
Funding: NVKP_16-1-2016-0004, K131458, FK20_ 134253, H2020 grant (SGA No. 739593)
Semmelweis University, Doctoral School of Pathological Sciences