Outcomes of Therapies and Resistance Mutations Following Non-Covalent Bruton's Tyrosine Kinase Inhibitor Treatment for Patients with Chronic Lymphocytic Leukemia and Richter Transformation

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washington; swedish; swedish cancer


Background: Non-covalent Bruton's Tyrosine Kinase inhibitors (ncBTKi) have shown excellent clinical activity for patients (pts) with relapsed and/or refractory chronic lymphocytic leukemia (CLL) and Richter Transformation (RT). However, some pts treated with ncBTKi develop progressive disease (PD). In addition, acquired BTK mutations (mut) at the time of PD on ncBTKi were recently described, although the frequency at which these mut occur has not been reported. Currently, data regarding treatment sequencing post ncBTKi are lacking but are critical to guide further treatment selection.

Methods: We conducted a retrospective, multicenter study of pts treated with any ncBTKi for CLL or RT who have discontinued ncBTKi for any reason. Using a standardized template we collected: pt and disease characteristics (including prior therapies, cytogenetic/molecular characteristics), demographics, clinical response to ncBTKi and subsequent therapies, and survival. Data on 2 lines of therapies (LOT) following ncBTKi were collected for each pt. Primary endpoint was overall response rate (ORR) for therapies following ncBTKi. Progression free survival (PFS) was estimated using the Kaplan Meier method. We also collected next generation sequencing (NGS) data for CLL pts who discontinued ncBTKi. Analyses were performed using STATA 17.0.

Results: We identified 63 pts (48 CLL, 15 RT) treated with who then discontinued ncBTKi. Baseline characteristics at ncBTKi start are presented in Table 1. Median number of prior therapies was 4 (1-10), and most pts received prior covalent BTKi (93.7%) and venetoclax (57.1%). At ncBTKi start, 84.8% of patients had unmutated IGHV, 48.8% had a TP53 mut and 37.0% had a complex karyotype.

ORR to ncBTKi was 58.8% for the CLL cohort (PR 54.4%, PR-L 4.4%) and 46.7% for the RT cohort (CR 6.7%, PR 40%). Median duration of ncBTKi exposure prior to discontinuation was 9 (1-27) and 4 (1-12) months for CLL and RT, respectively. Overall, 73.7% of the combined cohort progressed on ncBTKi. Specific reasons for ncBTKi discontinuation included: CLL PD (n=26, 41.2%), PD of existing RT (n=7), death not secondary to PD or toxicity (n=6), other reason (n=6), stem cell transplant (SCT, n=5), toxicity (n=4), PD of CLL to RT (n=4), MD/pt preference (n=2), CAR T (n=2), and sudden death on therapy (n=1).

Following ncBTKi, 76.2% of pts (n=48) received another LOT. Therapies and responses are presented in Table 1. Common treatment strategies were: chemo+/-immunotherapy (CIT) (n=16, ORR 18.8%), CD19-directed CAR T-cell therapy (n=7, ORR 85.7%), allogeneic SCT (n=6, ORR 83.3%), and venetoclax-based therapy (n=10, ORR 70.0%). 27.3% of therapies administered post ncBTKi were administered on a clinical trial.

For CLL pts, median PFS for first LOT following ncBTKi was 14 months (n=25 pts, Figure 1). For the RT cohort, the median PFS for the first LOT following ncBTKi discontinuation was 6 months (median follow-up 2.5 months). Importantly, median PFS for venetoclax following ncBTKi discontinuation for CLL pts was 14 months (8 pts, 87.5% venetoclax-naive, median follow-up 10.5 months). 49.2% of the overall cohort has died, with 58.6% of deaths due to CLL or RT (n=17 of 29 pts with available data).

15 CLL pts who discontinued ncBTKi for PD had end of treatment NGS data available. For these pts, at the start of ncBTKi, BTKC481 mut and PLCG2 mut were present in 38.5% and 33%, respectively. At end of ncBTKi treatment, novel (not C481) BTK mut were identified in 9 of 15 pts (60.0%). These included mut in BTKL528W (n=6), BTKV416L (n=2) and BTKT474I (n=2); 1 pt had mut in both BTKT474I and BTKL528W. Additionally, 4 pts had pre-existing mut in PLCG2 that persisted at PD. Overall, 11 of 15 (73.3%) of CLL pts had a novel BTK mut and/or a persistent PLCG2 mut at PD on ncBTKi.

Conclusions: We report results from the first series of CLL and RT pts following ncBTKi discontinuation. CIT for RT and CLL yielded poor outcomes, while CAR T-cell therapy and allogeneic SCT had high ORR warranting further investigation. Most importantly, venetoclax has clinical activity (high ORR, durable PFS) for CLL pts following ncBTKi discontinuation suggesting CLL pts can stay within the BTKi class prior to switching to venetoclax. In addition, at PD 73% of pts had a novel BTK mut and/or the persistence of a PLCG2 mut conferring resistance to ncBTKis. Overall, these results highlight an unmet need for novel therapeutic strategies for pts who require treatment following ncBTKi.

Clinical Institute