Research on cohort of patients relapsed on bruton tyrosine kinase inhibitors (btki)

Introduction: Acquired BTK/PLCG2 mutations remain to be the driver of drug resistance. The underlying mechanisms need to be further explored. In this study, we retrospectively analyzed the clinical and biological characteristics of fifty-five BTKi-resistant CLL patients in our center and mapped the mutational landscape. Method: Fifty-five CLL patients who relapsed on BTKis were included and analyzed. 31 patients had matched sequencing data. High sensitivity droplet digital PCR (ddPCR) was additionally used for the detecting certain BTKC481S mutation. Result: The median age at the time of progression on BTKis was 57 years (Table 1). 86.3% (44/51) pts were IGHV unmutated. The most commonly used fragments were 1–69 (n = 10), 4–39 (n = 9), 3–9 (n = 6), and 3–48 (n = 6) (Figure 1). Resistance to BTKi occurred at a median exposure of 27.6 m in our cohort, medium exposure were 11.23 and 30.59 m for Richter transformation and CLL progression, respectively, p < 0.001). At progression time, 46.9% (23/49) had TP53 mutation, 24.5% (12/49) had ATM mutation, 22.4% (11/49) had EGR2 mutation, 22.4% (11/49) had SF3B1 mutation, 16.3% (8/49) had NOTCH1 mutation, and 10.2% (5/49) had KMT2D mutation. Mutational landscape is shown (Figure 2). No significant shift of mutation landscape was shown between these two timepoints. By integrating NGS and ddPCR results, BTK/PLCG2 mutation was detected in 49.0% (24/49) pts. ddPCR method may not available for the patients relapsed on the Ibrutinib, this may account for the low rate of acquired mutations detected in patients treated with Ibrutinib. Besides, spatial clonal heterogeneity affect the detection of acquired mutations. In 2 pts presented as LN enlargrment at progression, acquired mutations were not detected by NGS (bone marrow sample) while mutation was detected by ddPCR method or lymph node sample was used. The most common mutation was C481S (Figure 3), other mutations at the C481 site include C481R, C481Y, C481F. BTK T474 and L528 mutation were also found, concurrent with BTK 481 mutation or alone. 4 patients had PLCG2 mutations, including one concurrent with BTK mutation. TP53 mutations were analyzed among pts with paired gene mutation results. 16/31 pts were TP53 wildtype at both timepoints. No significant differences in TP53 mutation burden were shown (Figure 4). 4 pts gained TP53 mutation at disease progression, including one carried two different clones. 8/11 pts showed a reduction of existing clone (including 2 disappeared); 2 showed an expansion of existing clone; 1 carried a stable clone at low VAF (detected by ctDNA). Conclusion: IGHV unmutated status was dominant in our cohort and the most frequently used fragment were 1–69(n = 10), followed by 4–39(n = 9). Acquired BTK/PLCG2 mutations remained to be factors of BTKis resistance and the most common mutation was C481S in our cohort. No significant difference in TP53 mutation burden was found during the treatment of BTKis. The research was funded by: This study was supported by National Natural Science Foundation of China (Grant No. 82170166, No. 82100207, No. 82170186, No. 81970146, No. 81900167), Translational Research Grant of National Clinical Research Center for Hematology (2020ZKZB01), Six Talent Peaks Project in Jiangsu Province 2019 (Grant No. WSN-001) and Youth Talent support Project in Jiangsu Province Hospital (Grant No. YNRCQN035). Keywords: chronic lymphocytic leukemia (cll), molecular targeted therapies No conflicts of interests pertinent to the abstract.