A phase II study of the selective phosphatidylinositol 3-kinase delta (PI3Kδ) inhibitor idelalisib (GS-1101) in combination with rituximab (R) in treatment-naive patients (pts) ≥65 years with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL).

Abstract

7005 Background: PI3K-delta is critical for activation, proliferation and survival of B cells and plays a role in homing and retention in lymphoid tissues. PI3Kδ signaling is hyperactive in many B-cell malignancies. Idelalisib is a first-in-class, selective oral inhibitor of PI3Kδ. When combined with R in 19 relapsed/refractory patients with CLL, the ORR was 78% (Coutre, ASH 2012). Methods: Treatment-naive pts ≥65 yrs with CLL or SLL were treated with R 375 mg/m2 weekly x 8 and idelalisib 150 mg bid continuously for 48 weeks (primary study). Pts completing 48 wks w/o progression could continue to receive idelalisib on an extension study. Responses and progression were based on investigator assessment using IWCLL criteria (Hallek, Blood 2008). Results: Data is presented here on the first 50 of 64 pts enrolled, 48 CLL/2 SLL, median age 71 yrs (range: 65-89), M/F 70/30 (%), Rai stage III/IV 10/32 (%), nodes ≥5 cm in 16%, WHO 0/1/2 in 34/64/2 (%); del(17p) in 6 pts and del(11q) in 13 pts. 32 pts completed 48 wks (18 discontinued, 11 due to AE, 4 due to death and 3 other); 30 pts entered the extension study and 26 remain on treatment. The median time on treatment was 16 months (range 0.8-27.5). The ORRwas 96% with 4% nonevaluable; median time to response was 1.9 mos (range 1.0-6.5). There have been no on-study relapses. The Kaplan-Meier estimated PFS is 91% at 24 mos. Of note, 6/6 pts with del(17p) responded (1 CR, 5 PR) and 3 remain on treatment for more than 21 months. 13/14 (93%) pts with thrombocytopenia and 12/12 (100%) pts with anemia at baseline responded. Of 20 pts with B symptoms at baseline, 13 (65%) were asymptomatic by 8 wks. Most frequent AEs (total%/ ≥G3%) were diarrhea (including reported as colitis) (46/16), pyrexia (42/4), chills (34/0), fatigue (34/2), rash (34/10), pneumonia (30/20) and nausea (28/0). Elevated ALT/AST was seen in 60%, Gr ≥3 in 22%. Conclusions: Idelalisib + R is highly active, resulting in durable disease control in treatment-naïve older pts with CLL. These results support the further development of idelalisib in frontline CLL. Clinical trial information: NCT01203930.