Predictive Significance of Selected Gene Mutations Identified Using Next Generation Sequencing in Relapsed and Refractory Chronic Lymphocytic Leukemia Patients Treated with Ibrutinib

Ibrutinib, a selective inhibitor of the Bruton's kinase (BTK), is characterized by high efficacy in the therapy of treatment-naïve and relapsed and refractory chronic lymphocytic leukemia patients (RR-CLL). Numerous clinical trials and "real-world evidence" confirmed its clinical efficacy also in high-risk patients, including those with TP53 aberrations. Predictive factors to ibrutinib therapy present at time of treatment initiation are not well recognized, therefore we aimed at analyzing the potential significance of mutational status of selected 22 genes in the disease outcome. For this purpose, targeted sequencing of approx. 2 Mb of exonic regions was carried out in 45 RR-CLL patients using custom-made gene panel and sequencing on Illumina MiSeq FGx platform (median 73x mean coverage, range 21.23-149x). Median patient age was 65 years, 28 (62.2%) patients were male and 25 (55.5%) patients had Rai 3-4 stage at ibrutinib initiation. Mean observation time was 34.5 (±19.9 SD) months, while ibrutinib was administered for the mean time of 33.8 (±20.8 SD) months. Median progression-free survival (PFS) and overall survival (OS) was not reached. The 36-month estimated rate of PFS and OS was 79.1% and 68.2%, respectively. The overall response rate (ORR) was noted in 23 patients (51.1%). Complete remission was noted in one (2.2%) patient, while partial remission and partial remission with lymphocytosis was noted in 16 (35.6%) and 6 (13.3%) patients, respectively. Twenty (44.4%) patients had stable disease, whereas progression following ibrutinib initiation was noted in 2 (4.5%) cases. The highest rate of pathogenic gene mutations was observed in TP53 (n=18; 40.0%), NOTCH1 (n=13; 28.8%), SF3B1 (n=11; 24.4%), ATM (n=7; 15.6%), MED12 (n=6, 13.3%), CHD2 (n=5; 11.1%), XPO1 (n=5; 11.1%), NFKBIE (n=5; 11.1%), BIRC3 (n=4; 8.9%), SPEN (n=4; 8.9%), POT1 (n=4; 8.9%), EGR2 (n=3; 6.7%), RPS15 (n=3; 6.7%). Single cases of mutation in ZMYM3, PIM2, PIM3, BRAF, RB1, TNFAIP3 were detected. No mutations in MYD88, BTK or BCL2 were detected. Univariate survival analysis revealed that none of the analyzed mutations had predictive significance in the analyzed group. Interestingly, ibrutinib treatment was characterized by stable PFS and OS despite the low ORR levels with a significant number of patients achieving disease stability.