A Phase Ib/II Study of Ibrutinib in Combination with Obinutuzumab-Gazyva As First-Line Treatment for Patients with Chronic Lymphocytic Leukemia > 65 Years Old or with Coexisting Conditions

Standard treatment for patients with chronic lymphocytic leukemia (CLL) is rapidly evolving and gradually has incorporated the combined use of monoclonal antibodies (mAbs) and targeted therapy with small molecules. Single agent Ibrutinib (Ibr), a first-in-class BTK inhibitor, is effective in previously untreated patients including those that are older than 65 or considered unfit to receive chemotherapy-based combinations. The complete response rate in patients receiving single agent Ibr is relatively low (overall response rate of 86% and complete response of 4% based on 2008 iwCLL criteria), though most patients have durable remissions. The combination of Ibr with mAbs like Obinutuzumab-Gazyva (G), a third-generation anti-CD20 mAb, can ameliorate the Ibr-induced lymphocytosis and increase the overall and complete response rates. Accordingly, we initiated an open-label phase Ib/II clinical study of Ibr in combination with G for first-line therapy of previous untreated pts with CLL.

The study completed enrollment of 32 previously untreated patients with CLL. Patients received G administered based on FDA dosing recommendations for 6 cycles (28 days/cycle) and Ibr 420mg po (1-3 hours before starting G infusion), and daily for up to 3 years. All patients received prophylactic medications. Patients were assessed for response by 2008 iwCLL criteria two months after completion of G, as the primary efficacy endpoint.

The median age of the patients was 65 (range: 46-78) years. 84% of the patients had a CIRS >6, 45% had a Rai stage III-IV and 19% had an ECOG performance ≤2. The median baseline absolute lymphocyte count (ALC) was 79x10³/mm³(range: 1.4-412.4). Patients showed the following FISH/cytogenetic abnormalities: del(13q) in 55%, trisomy 12 in 23% and del(11q) in 19%. Only 2 (6%) of these patients showed del(17p). From the patients with IGVH mutational status available (n=17), 11 (65%) were unmutated (>98% homology).

Most adverse events (AEs) were grade 1-2 (74%). Six patients (19%) had grade 1-2 G-infusion-related reaction (IRR) and only one patient (3%) showed grade 3 IRR (without the need for G discontinuation). We observed neutropenia (all grades: 52%, grade 3-4: 23%), thrombocytopenia (all grades: 71%, grade 3-4: 19%) and anemia (all grades: 26%). There were no cases of febrile neutropenia. Two patients (6%) had grade 1 bleeding (one patient with asymptomatic lower gastrointestinal bleeding and the second patient with epistaxis) that resolved spontaneously without requirement of blood transfusion or study treatment discontinuation. Two patients (6%) developed pneumonia, one was community-acquired pneumonia requiring inpatient treatment with IV antibiotics; the study treatment was held until resolution of symptoms and re-initiated at full dose. The most frequent non-hematological AEs were diarrhea, transaminitis, hyperbilirubinemia, hyperglycemia, and electrolyte alterations (grade 1-2). Three patients (9%) discontinued Ibr due to atrial fibrillation grade 1 (n=1), rash and headaches grade 2 (n=1), and persistent grade 4 thrombocytopenia (n=1).

Twenty-three patients were evaluable for response assessment by 2008 iwCLL criteria (median follow-up of 11 months). 84% of the patients showed a rapid decrease in ALC from baseline during the first cycle of treatment and only four patients (13%) required more than 3 cycles of treatment to achieve an ALC response. The overall response rate was 100%. The majority of pts had a partial response and six of 23 evaluable patients (26%) achieved a complete remission with detectable Minimal Residual Disease in the bone marrow by multiparametric flow cytometry.

In summary, Ibr-G combination has been generally well tolerated. AEs have been consistent with the known safety profiles of Ibr and G individually. The patients that discontinued Ibr remain in follow-up without disease progression. 100% of evaluable patients achieved response after 6 months of combination therapy, and 26% of patients met CR criteria. One important finding thus far has been a very low rate of IRR, (19% grade 1-2 and 3% grade 3-4), suggesting that Ibr can strongly mitigate the incidence and severity of G associated IRR.