Gilead announced results from Study 101-08, a Phase 2 study which is evaluating idelalisib (formerly GS-1101), an investigational, targeted, highly selective oral inhibitor of phosphoinositide 3-kinase (PI3K) delta, in combination with rituximab for older patients with treatment-naïve chronic lymphocytic leukemia (CLL).

Study 101-08 is an open-label, single-arm trial that enrolled 64 treatment-naïve patients ≥65 years old with CLL or small lymphocytic lymphoma (SLL). Patients received intravenous rituximab 375mg/m2 weekly for eight weeks and oral idelalisib 150mg twice daily for 48 weeks. The primary endpoint of the study is overall response rate (ORR), defined as the proportion of patients achieving a complete or partial response with this regimen. Patients completing 48 weeks of therapy without progression could continue to receive idelalisib in an extension study.

This regimen achieved a complete response (CR) rate of 19% and an ORR of 97% with estimated progression-free survival (PFS) at 24 months of 93%.The median time on treatment was 14 months, with 40 patients entering the extension study and 33 patients remaining on treatment. The median time to response was two months. No relapses were reported. Nine patients with chromosome 17p deletion (del 17p) (n=6) or mutation in the TP53 gene (n=3), which have been linked to poor prognosis, all responded to therapy including three with a complete response. Ninety-four percent of patients with thrombocytopenia at baseline responded to treatment (16/17), as well as all patients with anemia at baseline (17/17).

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