Idelalisib Plus Anti-CD20 Used Second Line Shows Improved PFS and Comparable Safety Compared to Later Line Therapy of Relapsed CLL

Introduction: Idelalisib (IDELA) is a first-in-class PI3Kδ inhibitor that is approved for use in combination with rituximab for patients with relapsed or refractory chronic lymphoid leukemia (R/R CLL) in the United States and in combination with rituximab or ofatumumab for the same indication in the European Union. Clinical trials evaluating IDELA in the first line setting for CLL were prematurely terminated due to an increased incidence of serious adverse events (AEs) and mortality; therefore, IDELA is not indicated as a first line therapy for CLL. The safety signal observed in the treatment naïve setting has produced a prevailing view that early line use of IDELA may also lead to inferior clinical outcomes. To address this question, we evaluated the clinical benefit:risk balance for IDELA in early vs. later lines of use in the relapsed setting.

Objective: To investigate clinical outcomes across sub-populations of IDELA + anti-CD20-treated patients with R/R CLL based on number of prior chemo-immunotherapy treatment regimens.

Methods: Using clinical outcomes data collected in Gilead-sponsored clinical trials of patients with R/R CLL treated with IDELA + anti-CD20 (312-0116/0117, N=110, Furman et al., N. Engl. J. Med. 2014; 370:997-1007, and 312-0119, N=173, Jones et al., Lancet Haematol. 2017; 4:e114-e126), we retrospectively compared the overall response rate (ORR), progression-free survival (PFS), overall survival (OS), and AE profile for patients previously treated with 1 prior regimen (IDELA given in the second line setting, 2L), 2 prior regimens (3L), or ≥3 prior regimens (≥4L). PFS and OS were estimated using the Kaplan-Meier method and groups were compared using a log-rank test. The incidence of AEs was compared using the Kruskal Wallis test.

Results: Among 283 patients treated with IDELA + anti-CD20, 49 (17.3%) received IDELA 2L, 69 (24.4%) received it 3L, and 165 (58.3%) received it ≥4L. Patient characteristics were similar except that patients in the ≥4L group presented with Rai stage III/IV disease more frequently compared to the 2L and 3L groups (70.3% vs. 61.3% and 57.9%, respectively, Table 1). ORR was similar irrespective of the number of prior regimens (85.7% for the 2L group, 73.9% for the 3L group, and 80% for the ≥4L group, p=0.2866); however, PFS and OS were longer in the 2L group compared to the 3L and ≥4L groups (median PFS= 31.5 months, 16.6 months, and 17.3 months, respectively, [Figure 1] and median OS=47.4 months, not reached (NR), and 34.6 months, respectively). No statistically significant difference was observed across treatment setting groups in the incidence of grade 3/4 key treatment-emergent AEs, including cough, diarrhea, infection, transaminitis, and colitis (Figure 2).

Conclusion: These analyses indicate that patients with R/R CLL experience comparable or improved efficacy and have a similar safety profile when IDELA + anti-CD20 regimens are used 2^nd line as compared to later line, after chemo-immunotherapeutic regimens. The longer PFS and OS times for patients treated with IDELA in the 2L may reflect shorter time since diagnosis, lower stage disease, or less disease resistance in this group, but also suggest that the efficacy benefit of IDELA + anti-CD20 is greater and may therefore better offset the potential toxicity in this patient sub-group. These findings support the use of IDELA + anti-CD20 in the 2L+ setting for patients with R/R CLL following chemo-immunotherapy.

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