Clinical improvement with a novel CD20 mAb, ofatumumab, in fludarabine-refractory chronic lymphocytic leukemia (CLL) also refractory to alemtuzumab or with bulky lymphadenopathy

Abstract

7043 Background: Patients (pts) with CLL refractory tofludarabine and alemtuzumab (double-refractory, DR) or refractory to fludarabine with bulky (>5 cm) lymphadenopathy (bulky fludarabine-refractory, BFR) have a poor prognosis. Ofatumumab is a human mAb specific for a distinctive small-loop epitope of CD20 that appears more potent than rituximab in eliciting complement-dependent lysis of B cells in vitro. We report, for the first time, results from the planned interim analysis of the clinical benefit observed in pts with DR or BFR CLL treated with ofatumumab in an international pivotal clinical study. Methods: Pts with DR or BFR CLL received 8 weekly then 4 monthly ofatumumab infusions (Dose 1, 300 mg; Doses 2–12, 2,000 mg). Primary endpoint was overall response rate (ORR; 1996 NCI-WG criteria), as assessed by an Independent Review Committee, over 24 wks. Results: Of 138 treated pts (DR: N = 59; BFR: N = 79; median age 64 and 62 yrs, respectively), 63% had Rai stage III/IV disease at screening. Pts had a median of 5 prior therapies. ORR (99% CI) was 58% (40, 74%) in the DR and 47% (32, 62%) in the BFR groups, and median overall survival (95% CI) was 13.7 mo (9.4, NR) and 15.4 mo (10.2, 20.2), respectively. Resolution of disease symptoms (maintained for ≥2 mo) were observed in a large proportion of pts (Table), including in pts considered nonresponders by NCI-WG criteria. Improvements in hematologic values were also observed in some pts with abnormal baseline values, particularly for platelet counts. Pts with thrombocytopenia at baseline (n = 73) experienced sustained increases in median platelet counts from 65 × 109/L to over 100 × 109/L by Wk 8; a similar pattern of rapid improvement was observed in Hgb values. Conclusions: Ofatumumab as single-agent achieves high ORR, and improves disease symptoms and hematologic parameters in heavily pretreated pts with DR and BFR disease who lack standard treatment options. [Table: see text] [Table: see text]