The Bruton's Tyrosine Kinase (BTK) Inhibitor PCI-32765 Induces Durable Responses in Relapsed or Refractory (R/R) Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma (CLL/SLL): Follow-up of a Phase Ib/II Study
Authors: O'Brien Susan , Burger Jan A. , Blum Kristie A. , Furman Richard R. , Coutre Steven E. , Sharman Jeff , Flinn Ian W. , Grant Barbara , Heerema Nyla A. , Johnson Amy J. , Navarro Tasheda , Holmgren Eric , Hedrick Eric , Byrd John C. 
Published: October 2019

Abstract
Abstract 983

Introduction:
Btk is a central mediator of B-cell receptor signaling which is essential for normal B-cell development. PCI-32765 is an orally-administered irreversible inhibitor of Btk which induces apoptosis and inhibits cellular migration and adhesion in malignant B-cells. An early analysis of the phase Ib/II study PCYC-1102 showed PCI-32765 to be highly active and tolerable in patients with CLL (Byrd, ASCO 2011). Here we report longer-term follow-up of this multicenter phase Ib/II trial.

Methods and Patients:
Two cohorts of CLL patients (previously untreated ≥65 years old and relapsed/refractory [R/R] disease following at least 2 prior therapies, including fludarabine) were treated with oral PCI-32765 administered daily for 28-day cycles until progression of disease. Doses of 420mg (previously untreated and R/R) and 840mg daily (R/R) were examined. The patients with R/R disease are the subject of this report.

Results:
Sixty-one R/R CLL/SLL patients were enrolled (420mg cohort n=27, 840mg cohort n=34). The median follow-up time for the 420mg cohort is 10.2 months and for the 840mg cohort is 6.5 months. The median number of prior treatment regimens for the 420mg cohort was 3 (2–10) and for the 840mg cohort was 5 (1–12). Seventy-two percent of patients had at least one poor-risk molecular feature: del(17p) 31%, del(11q) 33%, IgVH un-mutated 57%. Treatment has been well tolerated. Two patients have discontinued for adverse events (AE); 6 patients have required reduction of PCI-32765 dose (420mg cohort 2/27, 840mg cohort 4/34). Grade 1 or 2 diarrhea, fatigue, nausea, and ecchymosis have been the most frequently reported AEs. Serious AEs (SAEs) have occurred in 38% of patients; SAEs considered potentially related to PCI-32765 have occurred in 10% of patients. Grade ≥3 AEs considered potentially related to PCI-32765 occurred in 21% of patients. A characteristic pattern of response, with a transient phase of lymphocytosis typically peaking within the first 2 months of Rx, followed by resolution over time, has been observed in the majority of patients. Objective response (ORR; PR + CR) by IWCLL criteria in the 420mg cohort cohort, previously reported as 48% with 6.2 months median follow-up (Byrd, et al ASCO 2011), is now 70% with 10.2 months median follow-up. ORR in the 840mg cohort is 44% at 6.5 months median follow-up. An additional 19%, and 35% of patients in these cohorts, respectively, have a nodal PR (>50% reduction in aggregate lymph node size) with residual lymphocytosis. ORR appears to be independent of molecular risk features. Eighty-two percent of patients (50/61; 420mg cohort 22/27, 840mg cohort 28/34) remain on PCI-32765. Only 8% (5/61) of patients have had progressive disease (PD); 6-month PFS is 92% in the 420mg cohort and 90% in the 840mg cohort. Treatment cessation not related to PD or AE includes: death (n=2) or investigator discretion (n=3).

Conclusions:
The potent Btk inhibitor PCI-32765 is well tolerated and is associated with high rates of 6-month PFS in R/R CLL/SLL. Phase III trials of PCI-32765 in CLL/SLL are planned.

Disclosures:
O'Brien: Pharmacyclics, Inc: Research Funding. Burger:Pharmacyclics, Inc: Research Funding. Blum:Pharmacyclics: Research Funding. Furman:Pharmacyclics, Inc: Research Funding. Coutre:Pharmacyclics, Inc: Research Funding. Sharman:Pharmacyclics, Inc: Research Funding. Flinn:Pharmacyclics, Inc: Research Funding. Grant:Pharmacyclics, Inc: Research Funding. Heerema:Pharmacyclics, Inc: Research Funding. Johnson:Pharmacyclics, Inc: Research Funding. Navarro:Pharmacyclics, Inc: Employment, Equity Ownership. Holmgren:Pharmacyclics, Inc: Consultancy. Hedrick:Pharmacyclics: Employment, Equity Ownership. Byrd:Pharmacyclics, Inc: Research Funding.