Ofatumumab Based Chemoimmunotherapy (CIT) for Patients with Previously Untreated CLL

Abstract 3898 Background: Although chemoimmunotherapy (CIT) has substantially improved response rates, treatment free survival, and overall survival in patients with chronic lymphocytic leukemia (CLL), only 4050 of patients achieve a complete remission and the majority have residual disease when evaluated using sensitive assays. There remains interest in identifying new approaches to improve the effectiveness of CIT. Ofatumumab is a humanized anti-CD20 monoclonal antibody that is approved for patients with relapsed CLL refractory to fludarabine and alemtuzumab. The single agent activity of ofatumumab in patients with refractory CLL suggests it may have greater efficacy than rituximab in patients with CLL. To explore the efficacy of ofatumumab based CIT, we initiated a clinical trial studying the effect of ofatumumab in combination with pentostatin and cyclophosphamide (PCO) for patients with previously untreated CLL. METHODS: Eligible patients were previously untreated and had CLL in need of treatment according to the NCI-WG criteria (Blood 111:5446). The treatment schema included 6 cycles of ofatumuamb (300 mg on day 1 of cycle 1;1000 mg on day 2 of cycle 1 and day 1 of cycles 26) followed by pentostatin (2 mg/m2) and cyclophosphamide (600 mg/m2) administered every 21 days. All patients underwent complete response evaluation including evaluation for MRD using sensitive flow cytometry (Leukemia 21:956) at the completion of treatment. RESULTS: 33 patients were enrolled at Mayo Clinic and Duke University between 3/2010 and 9/2010. All patients were eligible for treatment and have completed active treatment. Clinical characteristics included: 76 male, median age 63 (range: 5083); intermediate Rai risk 27; and high Rai risk 73. On prognostic testing 33 were CD38, 48 Zap-70 , 58 IGHV unmutated, and 6 had high risk FISH (del 17p13; del 11q22). 26 of 33 eligible patients (79) completed all 6 cycles of PCO induction. Seven patients went off treatment early (toxicity: n5; refusal: n1; progression: n1). Adverse events deemed at least possibly related to PCO induction included 8 (24) patients with grade 3 hematologic toxicity and 5 (15) with grade 3 non-hematologic toxicity. The overall response rate to PCO induction was 94 (31/33) with 15 (45) CR/CRi, 5 (15) CCR, 9 (27) nPR, and 2 (6) PR. 2/10 (20) patients with CR9s tested for MRD were also MRD negative by 6 color flow cytometry analysis. Finally, we compared this cohort of patients treated with ofatumuamb-based CIT to our prior 108 patient cohort of patients treated with rituximab-based CIT both of which used an identical chemotherapy backbone (pentostatin and cyclophosphamide). Although the age, gender, ALC, and prognostic profile (CD38, ZAP-70, and IGHV mutation status) of treated patients were similar (all p0.3), the ofatumumab cohort included more advanced stage patients (Rai stage III/IV: 73 vs. 41 p0.002). Ofatumumab-based CIT appeared to be better tolerated than our previous experience with rituximab-based CIT (grade 3 hematologic toxicity ofatumumab-CIT 24 \({\scriptstyle \raisebox{1ex}{8$}\!\left/ \!\raisebox{-1ex}{$33$}\right.}\]\) vs. rituximab-CIT51 \({\scriptstyle \raisebox{1ex}{55$}\!\left/ \!\raisebox{-1ex}{$108$}\right.}\]\) , p0.009; grade 3 non-hematologic toxicity ofatumumab-CIT 15 \({\scriptstyle \raisebox{1ex}{5$}\!\left/ \!\raisebox{-1ex}{$33$}\right.}\]\) vs. rituximab-CIT 24 \({\scriptstyle \raisebox{1ex}{26$}\!\left/ \!\raisebox{-1ex}{$108$}\right.}\]\) , p0.34). Despite a higher proportion of Rai Stage III/IV patients in the ofatumumab cohort, the efficacy of ofatumumab-based CIT also compared favorably to our previous experience with rituximab based CIT (Table). CONCLUSION: Front-line ofatumumab-based CIT appears to be well-tolerated in patients with CLL. Compared to our historic experience with rituximab based CIT, ofatumumab-based CIT appeared to have less hematologic toxicity and improved efficacy. This trial has been expanded to provide a larger experience with ofatumumab-based CIT. Disclosures: Shanafelt:Hospira: Research Funding; Glaxo-Smith-Kine: Research Funding; Genentech: Research Funding. Off Label Use: Off label use of pentostatin and Ofatumumab. Lanasa:GlaxoSmithKline: Consultancy, Speakers Bureau. Zent:GlaxoSmithKline: Research Funding; Genentech: Research Funding; Genzyme: Research Funding. Tun:Celgene: Research Funding. Kay:Biothera: Research Funding; Clegene: Research Funding; Cephalon: Research Funding; Genentech: Research Funding; Glaxo Smith Kline: Research Funding; Hospira: Research Funding; Novartis: Research Funding; Supergen: Research Funding; Calistoga: Membership on an entity9s Board of Directors or advisory committees; Celgene: Membership on an entity9s Board of Directors or advisory committees; Emergent Biosolutions (Formerly Trubion): Membership on an entity9s Board of Directors or advisory committees.