A Phase II Trial of Ofatumumab In Subjects with Waldenstrom's Macroglobulinemia.

Waldenstrom's macroglobulinemia (WM) is an indolent B-cell lymphoma characterized by a heterogeneous population of lymphocytes, plasmacytoid lymphocytes and plasma cells with variable CD20 expression. Rituximab (R) achieves an overall response rate (ORR) of 25–50% in relapsed/refractory WM and is associated with IgM flares, manifested by a rapid rise in IgM, potentially leading to complications of hyperviscosity. Ofatumumab (OFA) is a fully human monoclonal antibody that targets an epitope encompassing both the large and small extracellular loops of CD20 and effectively induces complement-dependent cytotoxicity of B-lymphoma cells. OFA is approved for the treatment of fludarabine- and alemtuzumab-refractory chronic lymphocytic leukemia (CLL) and has demonstrated clinical activity in non-Hodgkin's lymphoma. Given the efficacy of OFA in CLL, with its decreased CD20 antigen density, similar to WM where CD20 is down-regulated with differentiation of cells into plasma cells, a Phase II, open-label, single-arm trial of OFA in patients (pts) with WM was initiated to examine the safety and efficacy of OFA in this population. We report data from a planned interim analysis, which was performed to examine IgM flare, toxicity and response data.

Pts (age ≥18 years) with WM requiring therapy by 2nd International Workshop on WM criteria were eligible. Pts received OFA 300 mg week 1 and 1000 mg weeks 2–4. Premedication included acetaminophen and antihistamine (all infusions) and glucocorticoid (infusions 1 and 2). Pts who experienced grade 3–4 infusion-related adverse events (AEs) during weeks 1 and 2 also received glucocorticoid during weeks 3 and 4. The primary endpoint was ORR assessed by 3rd International Workshop on WM criteria, and toxicity was assessed according to NCI-CTCAE, v3.0.

Fifteen pts were enrolled between March 2009 and January 2010. Median age was 59 years (range 43–85), and 9 pts were male. Pts had a median IgM level of 3.70 g/dL (range 1.21–6.62) and median hemoglobin (hgb) of 9.8 g/dL (range 5.3–11.7). Three pts were previously untreated; 12 pts had received a median of 3 therapies (range 2–5), including 11 pts who had received R, and 7 pts who had received a purine analog. Fourteen pts completed all 4 infusions of OFA. One pt withdrew from study after infusion 3 due to a drug-related serious AE (SAE). One pt had cryoglobulinemia, which interfered with IgM assessment. Of the 14 pts with evaluable IgM levels, 3 achieved partial response (PR), and 3 achieved minor response (ORR=43%) 8 weeks to 5 months after start of OFA therapy. One of 3 previously untreated pts and 5 of 12 relapsed pts responded. Four of 11 pts who had received prior R and 2 of 4 R-naïve pts responded. Five of 9 pts with IgM <4 g/dL and 1 of 5 pts with IgM >4 g/dL responded. Four pts with a median hgb of 8.0 g/dL (range 5.3–9.2) experienced ≥2.8 g/dL increase in hgb, including 3 pts who had >5 g/dL increase; median time to reach hgb ≥11.0 was 4 weeks. Infusion-related events occurred with dose 1 (300 mg) in 12 pts and with dose 2 (1000 mg) in 7 pts; all infusion events were grade 1–2 except 2 grade 3 events (rash, serum sickness). Nine pts developed 11 infections: 7 URI, 2 UTI, 1 sinusitis, 1 oral candidiasis (all grade 2). One pt developed grade 3 febrile neutropenia. Two pts developed SAEs possibly related to OFA. One pt developed grade 3 Coombs-negative hemolytic anemia after infusion 3 resulting in study withdrawal, and 1 pt with a baseline IgM level of 6.62 g/dL developed grade 3 renal insufficiency due to a rapid rise in IgM and cast nephropathy 6 weeks after starting OFA. One additional pt, with a baseline IgM level of 4.69 g/dL, developed a rapid rise in IgM and hyperviscosity symptoms. Both pts with a rapid rise in IgM underwent plasmapheresis with resolution of symptoms. No other OFA-related hematologic toxicity was observed.

OFA has an acceptable toxicity profile, although a rapid rise in IgM requiring plasmapheresis was observed in 2 pts with high baseline IgM levels. OFA shows clinical activity in pts with WM, including those who relapse after R therapy, with rapid improvement in hgb and slower reduction of IgM levels. Based on the acceptable safety profile in this study and the dose of OFA approved for refractory CLL, the study was amended to increase the OFA dose to 2000 mg and allow a 2nd cycle of therapy for pts who do not attain PR after cycle 1. Accrual to the amended study is ongoing.

Furman:GlaxoSmithKline: Consultancy, Speakers Bureau; Genentech: Consultancy, Speakers Bureau; Cephalon, Inc.: Speakers Bureau; Celegene: Consultancy; Calistoga: Consultancy. Off Label Use: Ofatumumab is an investigational anti-CD20 monoclonal antibody, currently under development for the treatment of B-cell malignancies (chronic lymphocytic leukemia, diffuse large B-cell lymphoma, Waldenstroms macroglobulinemia and follicular lymphoma) as well as autoimmune diseases (rheumatoid arthritis and multiple sclerosis). Switzky:GlaxoSmithKline: Employment, Research Funding; Genmab: Employment, Research Funding. Leonard:GlaxoSmithKline: Consultancy. Liao:GSK: Employment. Shah:GlaxoSmithKline: Employment; Genmab: Research Funding. Brownell-Buttich:GlaxoSmithKline: Employment. Lisby:Genmab A/S: Employment. Lin:GlaxoSmithKline: Consultancy, Employment.