A Phase II Trial of Ofatumumab for Older Patients and Patients Who Refuse Fludarabine-Based Regimens with Previously Untreated Chronic Lymphocytic Leukemia or Small Lymphocytic Lymphoma,

Fludarabine (FLU), cyclophosphamide and rituximab (FCR) or other FLU-based regimens have shown improvement in response rates, progression-free survival, and in some studies overall survival in patients with previously untreated chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). However, a randomized trial of older patients demonstrated no improvement in progression-free and overall survival with FLU-based therapy (Eichhorst BF, et al: Blood 114; 3382, 2009). A recent retrospective analysis of serial CALGB trials (Woyach J, et al: ASH 2011) confirmed the lack of PFS and OS advantage of fludarabine in elderly patients but did find benefit of the anti-CD20 antibody rituximab across all age groups. Ofatumumab (OFA) is a fully human immunoglobulin G1 kappa, monoclonal antibody that targets a unique epitope on the CD20 molecule. Pre-clinical data indicate that OFA has greater NK cell and monocyte-mediated killing, complement-dependent cytotoxicity and direct killing against CLL cells. Based on pre-clinical and clinical studies indicating possible increased efficacy of OFA in patients with CLL, our aim was to develop an antibody-only regimen for older patients and patients who refuse FLU-based regimens.

Eligible patients had previously untreated, symptomatic CD20+ B-cell chronic lymphocytic leukemia (B-CLL) or small lymphocytic lymphoma (SLL), ECOG PS of ≤ 2, and were either ≥ 65 years of age, or patients 18–64 years of age who had declined FLU-based regimens. All patients in this study received OFA as an IV infusion once weekly for a total of 8 weeks. To reduce the possibility of infusion reactions, the first dose of OFA was administered at a dose of 300 mg. If the initial 300-mg dose of OFA was well tolerated, without occurrence of any infusion associated AEs of ≥ grade 3, subsequent doses of OFA (i.e., Week 2 through Week 8) were given at a dose of 2000 mg. Eight weeks after the 8-week study treatment period ended, patients were assessed for response to the treatment. Patients who progressed received no further treatment. Patients who responded to the treatment or who did not have disease progression received maintenance therapy consisting of OFA at a dose of 2000 mg IV every 2 months for 2 years (for a total of 12 doses, in the absence of PD or intolerable toxicity) beginning 3 months after the last dose of OFA.

Between 8/2010 and 4/2011, 42 patients were enrolled and are included in this analysis. Patients were 57% male with median age 69 yrs (range: 47–88 yrs). Fourteen patients (33%) were < age 65. All but 1 patient had CLL; 1 patient had SLL. The median WBC at study entry was 41.1 (range 1.7–236.5). Rai stage at entry to study was Stage 0 = 8, Stage I = 8, Stage II – 4, Stage III – 10, Stage IV – 11. Interphase cytogenetics demonstrated 2/42 (5%) 17p-, 4/42 (10%) 11q-, 11/42 (26%) trisomy 12, 9/42 (21%) normal, 14/42 (33%) 13q-, and 2 (5%) unknown. To-date, 41 (98%) patients remain on study and 35 have completed 8 weeks of initial therapy with 24 (57%) having already begun maintenance therapy. Lymphocyte count normalized in 85% of patients at the end of the initial 8 weeks of therapy. Thirty patients have been evaluated for response according to IWCLL criteria (Hallek 2008): 13 patients (44%) achieved an objective response (CR, 0; PR, 13); 16 (53%) patients had SD; 1 patient (3%) had PD. SAEs were infrequent with 2 patients hospitalized for unrelated events: g2 fracture, g3 chest pain, g3 hematoma and g4 pulmonary emboli; 2 patients hospitalized for events possibly OFA-related had g2 fever, g3 anemia and g3 pneumonia. Only 1 patient experienced significant infusion-related toxicity that required repeat administration of the initial 300-mg dose instead of dose escalation at dose 2. Baseline FcγR polymorphisms for patients enrolled are currently being analyzed and will be presented.

Single-agent OFA is a highly active and well tolerated front-line therapy for older patients with CLL or patients refusing FLU as evidenced by both early response and also ability of virtually all patients to proceed to maintenance therapy. A low incidence of serious infusion toxicity, infectious morbidity and other heme / non-heme toxicities was observed. Continued long-term assessment will further characterize the toxicity and efficacy of this single-agent OFA regimen in patients with CLL, as well as overall and progression-free survival rates.

Flinn:GSK: Research Funding. Off Label Use: Ofatumumab in front-line CLL. Jones:Abbott Labs: Research Funding; GSK: Consultancy.